I don't think you guys are hitting the main issue - he's 6'7"! The most important thing is to find somebody who makes a bike in like an XXL or 23" or something - to at least get close to fitting you. I ride a 21 and I'm 6'4" w/ long arms. Its lovely to suggest rockhoppers or konas but w/o them comming in a large size its useless.
I'd search around for someone (trek/fisher, giant, specialized, etc) who makes a gigantic frame to start. A few years ago i know Fisher made an XXL in a few of their models. $500 is going to lock you into a component set pretty much, so from their, being a heavy guy, you'll just have to upgrade things you break.