A taxi from Lima Airport to Miraflores takes about 40 mins to an hour, depending on how fast your taxi driver is, traffic etc.

I always have a taxi pick me up and take me back and it costs between S/.35 and S/.45 (between 13 and 16 bucks-ish) The supposedly authorised taxi service from the airport is Taxis Verdes, as coincidence would have it, I have their number written on a bit of paper next to my lappy. it is +51 1 355 5555

Given my own preferred taxi driver gets waved on by the police when dropping me off, I presume that the guys hanging around outside domestic arrivals are indeed Taxis Verdes. They wear lanyards and ID badges, that's about as "above board" as you are going to get in Latin America.

Note taxis in Peru do not have meters as that would be too sophisticated so a price would normally be agreed before getting in the Taxi. This is probably less of a problem going than coming back. At the airport you have other taxi drivers over hearing your haggling. In Miraflores you may be invited to pay a gringo tax. You could also try saying "Johnny says it costs 35 to 45 Soles so get screwed innit?"

Your lads absolutely don't want to be hanging out on Lima's beach, Lima's beach isn't particulary pleasing, that and it is currently winter. If they want to go to see the Ocean then Parque del Amor is a far more fitting place, on the cliff overlooking the beach. It also has parapenting if they are interested in that. From there they can walk to CC Larcomar, the apparent pride of the mirafloreņos but actually just a pretty lame collection of shops and restaurants wedged in the side of the cliff. If they don't fancy the romance and parapenting of Parque del Amor they could just go straight there.

From Larcomar they can walk up Av Jose Larco to Parque Kennedy and take in the cafe culture. If they want to have a nice mindblowing Peruvian lunch, they should go here http://puntoazulrestaurante.com/ which is halfway between Larcomar and Parque Kennedy