The hydor flo and SCWD are the cheapest wavemakers around. The hydor flo, at least the ones I had, tend to jam up or strip their gears after a few months. SCWDs generally are pretty good though.
I think best bang for the buck though is the Ocean Motion squirt. Takes a bit more plumbing but you can run it off any pump you want and it redirects the flow to 4 different outlets in a variety of patterns.