I almost fell over on this one. The author took a grinder, and basically added a joiner blade to it and a jig to make it into a biscuit jointer. And it seems to work pretty good. grinders at Harbor frieght run $60–80 dollars, the grinder is $10 and the blade is another $10….
http://www.instructables.com/id/Biscuit-Joiner-From-a-Grinder/