I bought the bike complete (MkIII Expert). My M.O. is to strip the bike down, sell off the drivetrain on eBay (well, in this case, the drivetrain along with everything else), and offset the cost of the new bike.

You'd probalby be surprised: with the right parts spec (usually an XT-level build), and the right price on the complete bike, a frame can often be had for anywhere from $0 to $200 after selling off all the parts that come with it on the complete bike. Makes frame upgrades somewhat cost effective.