newcastle

$5,000 is obscene. Absolutely unnecessary.

You can very easily, even as an inexperienced traveler, do this much more affordably and on your own. Due to your time restrictions, I'd say the bus is out. No big loss, as you can do a low cost airlines for not much more and 1/10th of the time. Your best bet from Lima to Cusco will be on StarPeru or Peruvian Airlines. Once in Cusco you can buy your own train ticket (very simple), choose your own lodging (no lack of choices at any budget level), and get yourself to MP without anyone's help. Private message me if you'd like and I'd be glad to help you. Or, check out a Lonely Planet book and it details the do it yourself process step by step. You can probably even buy a pdf of that specific chapter online.

MarLim

Train and Entry into MP cost about USD 200/pp depending on the type of train you take. Keep in mind, that you have to buy MP entry tickets before accessing the site, preferably via internet. You can also buy tickets either in Cuzco or in Aguas Calientes, but since a couple of months there is a daily limit of tickets sold, so I strongly advice to buy in advance not to arrive in Cuzco just to realize that you can't go to MP because the limit has already been sold. Same for trains, reserve in advance. You can all do by yourself via internet.

As far as hotels are concerned, I'd stay 2 nights in Ollantaytambo, this is about 400-500 attitude meters lower than Cuzco and will help you to acclimatize to the height (soroche headache). Trains to/from MP leave in Ollantaytambo. There is a good hotel just beside the train station, which is very convenient if you leave early in the morning and come back late in the day. You ideally fly into Cuzco in early afternoon, take a taxi or combi to Ollantaytambo, next day MP, the day after Cuzco and back to Lima in the evening. Be aware that Cuzco airport can have heavy fog and flights may get cancelled. Allow for some cushion to your next flight out of Lima.

While MP and Cuzco are cerlainly more interesting than Lima, be aware, that February is one of the best months to explore Lima, but not for Cuzco and MP where you can find heavy rain and clouds.

FrogProf

I lead groups of students to Santiago twice per year. The first day of the trip, the students play the "Santiago City Game." I thought you might like to see the list of visits/activities:

Climb Santa Lucia hill (Cerro Sta. Lucía) – to the top - and take a picture with the Universidad Católica in the background across the road.

Visit the Museo Chileno de Arte Precolombino.

Go to the Plaza de Armas (Main Square) and take a team picture with Pedro de Valdivia on his horse.

Visit La Moneda Palace and take a picture of the artwork in the courtyard.

Visit Catedral Metropolitana in the Plaza de Armas.

Visit Museo de Bellas Artes.

Go to the Lastarria Neighborhood and take a picture at Plaza Mulato Gil.

Visit the Parque de las Estatuas (Park of the Statues) and take a picture with two statues.

Climb or descend San Cristóbal Hill on the Hill Train (Funicular).

Visit La Chascona museum.

Climb to the top and take a picture next to the Statue of the Virgin.

Buy some Mote con Huesillo at the shops below the Virgin’s Sanctuary.

Eastbay1K

You had me until the last stop. I've had this "delicacy" (well, tasted it) maybe 3 times in my life. This is not a reflection on the Virgin, who I'm sure gives the mote con huesillo some sainted quality. The fact is, there is no good recipe for this. Maybe if you thin it down with some Capel, it would help. On that note, I'm hoping no one pours me any vaina on New Year's Eve. Or more than a sip of cola de mono.

Otherwise, sounds like a fun day (that can be divided into 2 days).

OskiBear

I actually did a similar trip a few months ago. Different number of days in each of the locations but essentially the same. I'll try to answer the questions below:

Jax78

I love the idea of the "Santiago City Game" -- thank you for sharing!

I did wind up booking a side trip to MP, staying in Aguas Calientes and Cusco, including tickets for MP and Huanya Picchu.

I'm still feeling anxious about what to pack. I don't want to go out and buy a bunch of clothes I won't likely wear again but trying to wash and dry jeans will be a pain. So many things to think about!

ajginyul

You'll have a great trip! I realize you have already received a bunch of good replies, but below are my 2 cents -- hope it helps with regards to Chile and Argentina. I haven't been to Peru - yet.

First - about the clothing. In general, Chilean and Argentinean women wear tidier and more classic clothing than Americans. They can get relatively dressed up at night (eg., black pants, heels, stylish blouse and blazer, silk scarves, etc.) In Argentina especially the women are very stylish. (Just Google their president.) To blend in, try to wear classic and neat clothing, like long white or black pants or a knee-length skirt, classic blouse, a nice fitted t-shirt, etc. Have a nice light cardigan on hand or very lightweight (it will be hot) fitted jacket/blazer. Find a comfortable pair of flats and try to wear those instead of tennis shoes. You will, unfortunately, stick out and possibly attract unwanted attention if you wear shorts, casual t-shirts, casual sandals or tennis shoes. I also personally feel I'm sticking out if I wear bright clothes, so neutrals like black, white, and off-whites/beiges are ideal.

Minimal jewelry is worn in both countries. I just wear inexpensive earrings.

By the way I'd recommend wearing a purse with one of those long straps that goes over your shoulder and across your body.

1. YES. I recently spent 5 days in BA, and there's a lot to see and do if you love history and architecture. If you're a history/art/architecture buff, be sure to see: the Casa Rosada and step into the beautiful national cathedral, San Telmo especially on Sunday during the antiques market, walk along Corrientes and enjoy the bookstores and a cup of tea or coffee at El Gato Negro or any of the other "gran cafes", El Ateneo Grand Splendid bookstore, Evita Museum which is one of the most elegant museums I've been to. If you like shopping for clothes, accessories or trendy interior decor: Palermo Soho or Palermo Hollywood on a Saturday. Eat beef, Italian food (pastas, gelatos, coffee).

In Chile, try to eat local foods like seafood and enjoy the beautiful landscapes.

2. How common is Internet access, especially free wifi with lodging? I'm not sure what the practices are.
I find it varies by hotel, most hotels have WiFi, some include it for free. It's hard to find in cafes.

3. Is it crazy to bring 2 or 3 suitcases (for two people to share)?
No. Especially if you love shopping and you're going to BA

6. On that note, hotels in the US usually provide shampoo and conditioner. Is this common in SA, too, or do I need to make sure to have my own?
They should be provided by most standard hotels, although sometimes I find they are smaller portions than provided in US hotels.

7. Anything to make sure I bring from home that might surprise me? Like, should I be able to easily find Tums, Advil, feminine hygiene products, sunblock, or anything else like that?
I highly recommend bringing your own medicines, feminine hygiene products, and sunblock from home. Not only are they way more expensive in SA, harder to find (and you might have to ask someone for them in Spanish), different brands and the feminine hygiene products tend to be different. Note - shampoos, soaps and conditioners also smell quite different in some SA countries especially Chile, so if you are sensitive to smells (or prefer unscented) bring those items from home.

8. If you were going on a similar trip, how much USD cash would you carry? My preference would be to not rely on a bank/ATM in SA but it seems crazy to carry enough cash for 2.5 weeks.
Note that banks/ATMs are reasonably easy to find in Chile, hard to find in Argentina even downtown BA. In Argentina, you can usually pay in USD at most restaurants, stores (and sometimes there's a discount for doing so). Of course, carrying a lot of cash can pose risks. It's good to check if your hotel room will have a safe, because then you can leave some cash behind when you go out for the day.
By the way, using a credit card in Chile can be tricky, as they will often want to see a government ID. I didn't have problems using my CC in Argentina at places that accepted it - be sure to ask first, because many places won't accept CC and only accept cash.

9. I tend to take my laptop with me, but is this a bad idea? What about an iPad or netbook?
Totally up to you, but my recommendation is to take only one device and store it in a hotel room safe during the day to avoid worrying about it. I used my iPad on wifi in my hotel lobby and it worked well.

10. I have an iPhone on AT&T. What's the best way to go about getting a data/phone plan? Should I just get a prepaid phone? Is there one that would work across my whole trip?
Forget buying a pay-as-you-go voice or data plan in SA: you can only get one if you have a government ID ( visa or residency) (at least in Chile, I believe Argentina is the same). Plus, I believe you'd need a different prepaid phone/SIM card for each country you go to. Therefore, you should probably buy a roaming plan with AT&T or just rely on internet/Skype while you're gone, which is what I do.

ENJOY!

Eastbay1K

So funny - almost every single small hotel in Chile will have packets of Sedal (shampoo) in the bathroom. No separate conditioner. That, and mini packaged bars of Lux soap.