I highly recommend visiting Samara in the off-season (we went in October). Not only was there sun, but also solitude: We were some of the only people there. The beach is never-ending, the water refreshing, and the locals are eager for your business.
Tico farmers walk the beach with their horses to offer rides. Prices are cheap: $6/hour or $20 for an unlimited ride (again, in the rainy season). They will take you through the rainforest with monkeys screeching overhead to nearby secluded beaches. Or customize your tour to see what you'd like, from hidden waterfalls to turtle beaches.