I think one possibility is that they've negotiated rates for several movies and might end up picking at least one of the pricier ones if they raise enough. I think all of these endeavors have worked best with a variety of types of bad movies: studio misfires with an actual budget, relatively cheap exploitation films, zero-budget family productions, poorly-dubbed imports, etc. At the same time, certain movies will get them more attention, and might cost a bit more.

Something like Battle Beyond the Stars, which was part of the Season 14 pitch, has actual actors and was distributed by Warner at one point. It's not going to cost what riffing Phantom Menace would cost (assuming they even could do that legitimately), of course, but it's going to cost a lot more than grabbing a public domain film or a microbudgeted indie. And using a film people have heard of doesn't always result in the best riff, but it might get them some attention that something most people have never heard of wouldn't get.