My wife buys a couple of these a year when we head down to Greece. They are normally painted right out on the sea side on some boardwalk and they represent a romantic scene of some sort.
In Euro they normally run about 10-15 Euro each, so about 8-13 USD. No value other than to the person who collects them. My wife can not pass up such art, they do this in Italy and Spain as well, they are just cheaper in Spain and Italy and look better from Italy. Always the same thing though, some sort of romantic scene. In Italy and Spain they are mostly done by University students earning some extra cash, in Greece it is normally done by drug dealer and part time pimps.