Define inexpensive.
A lady has just put up a group trip to row across the Caribbean Sea. 14 people will row a double-hull boat over more than a month. They'll definitely need to desalinate sea water.
http://globetrooper.com/caribbean-sea-row-2012-barbados-jama...
Katadyn does desalinators for civilians.
http://www.katadyn.com/usen/katadyn-products/products/katady...