Zyzzyx Road grossed $30 in the box office, 0.0015% of it's $2,000,000 budget. Very low budget films, if they're good, can often be very profitable. El Mariachi cost a mere $7,000 to make, and grossed $2,040,920 at the US box office alone. The Blair Witch Project, which cost $35,000 to make (a huge part of that advertising, as far as I'm aware) has grossed an insane $248,300,000 worldwide. A lot of these films end up making back profits in video and DVD sales and TV liscensing though. There's quite a lot of even smaller films for which figures aren't even available. I can easily imagine that films like Bad Taste, The Evil Dead, Last House on the Left, Texas Chainsaw Massacre and I Spit on Your Grave, some of which were probably filmed for under $5000, (some of them probably less) have made absolutely ridiculous returns, profit-wise.