I've talked to a guy, and he tells funny stories about how far they could make their prize money stretch between the occasional wins. They'd sleep half a dozen guys in one cheap hotel room, occasionally camp outdoors, accept a little money from home, pile as many people as possible into 1 player's car, etc. I don't remember them mentioning anything about being sponsored. He and a friend traveled together quite a bit and often played doubles together as well as singles. They did say that they had an arrangement where they agreed to split ANY prize money that EITHER earned, so they'ed have a better chance of having at least a little bit of money coming in if either one of them won anything.
After tramping the world for a couple of years, he settled down and became a teaching pro.