I'm not really sure on prices (if I wanted to go, I didn't care), but there is a market, with local sellers, right at the PP, on the main drag, thru the resort. There is also a tram for 5CUC return, into the village of Guardalavaca, which takes you to a great craft market.
Yes, the catamaran is available thru the PP, as well as several different tours, to local villages, and cigar factories/sugar mills/ rum distillers... You can take your pick!