Everyone in Cozumel takes U.S. dollars. In fact, I have to think hard to recall the last time I saw a peso there. Paradise beach is actually free to use, but they charge $8 per person for use of the water toys and such. Not a bad deal. The place has bars and two restaurants. Unless you get a van, you will need two taxis for 6 people. The prices are set rates. They don't use meters. I forget exactly but I'd figure on $15-20 each way, per taxi. Taxis are always available at the beaches, so you don't need to fret about being stranded.