I'm no fan of Priceline for Paris. I think their neighborhoods, while accurate as shown on the website, are too big to gauge what part of the city you'll wind up in. Also, it seems many of the hotels they offer are large business hotels, rather than the smaller ones Paris is known for. And you are correct in assuming that the hotel is not obligated to provide anything not shown by Priceline when you make your bid. The Paris Priceline bids I've seen (not many) seem to come in at 10-20% off the hotel's non-refundable rate, which is not enough to get me to commit to a hotel unknown.

I visited a few Citadine properties a few years ago. They were pretty upscale, although they amounted to a large hotel room, sometimes with a second small room. I recall one that had only a hot plate and a small fridge, hardly what I expected based on their "Apartment" angle, And, as you noted, they're not cheap.

Paris has a ton of small hotels, and you should be able to find one that is basic but clean, safe and quiet in a good area of town for 100-150 euros. This may not be the best website to find hotels and get the info you need-I'd try Trip Advisor, Rick Steeves or this site:

http://www.bonjourparis.com/

You'll also find a lot of Paris links in the "sticky posts" at the top of Paris topic here on FT.

Your question on the AF bus is one I never thought of. I can't imagine they'd require a kid seat but I can't recall seeing any toddlers on there either so you never know. I sure wouldn't bring a seat just for that. If I were you, I'd try to use the AF bus-don't buy tickets ahead, just buy them from the driver after you confirm you don't need a seat. If there is any problem, you can always take the RER train into Paris.