In Cuba you're never far from a world class beach. Some of the most famous are located in Varadero and Guardalavaca on the north coast, but Trinidad and Cienfuegos on the south coast also have great beaches.
If you want solitude, Crusoe style deserted coast line and a feel of being on your own private beach, head to the Cayos of Santa Maria, Coco or Guillermo.
Even Havana, otherwise not known as a beach destination, has a strip of beaches 20 minutes outside town that will knock the socks off most tourists. How about spending a weekend there away from the city in your own beach house for 30-40 dollars per night?