With the exception of the jbird false bottoms (which I can't afford), it looks like all of the false bottoms for the 20/25gal kettles are the same. That said, the best price I can find at the moment is at morebeer.com for $95
Before I pull the trigger, I thought I'd see if anyone knew of a cheaper source.
I made my own from the bottom of a keg (i flipped the keg upside down to bottom drain the MLT). I hit it with a angle grinder, and 20 min later it was done. Not nearly as snazzy as dutchoven's (very nice job btw), and maybe a touch harder to use, but it works well enough.
p.s. if you make your own, don't drill the holes. It'll take forever. Cut slits in it.