Not that it's terribly helpful but a quick search on ebay shows a bunch of Rev. 6 A500 motherboards starting in the $60-$70 USD range. With the newer board it's just "pop right in", you don't have to do any soldering or modifications.
http://amiga.resource.cx/mod/a500.htmlYou also get to take advantage of the higher density ram chips & newer-model Agnus.
