A tale of two eBay auctions:
#7335975478: 'World's most modded TR606 drum machine!', ended July 10th 2005, 246 views, sold to twistedaudio for £350.
#7354365370: 'World's Most Modified Roland TR-606', ended October 6th 2005, 8811 views, mentioned by numerous blogs and message boards, sold by twistedaudio for £853.
Hmmm. I wish I'd spotted this at the time.
UPDATE: #7356203863: Either these things are being mass-produced, or a joker in Coopersberg PA is trying to sell the same unit. Bidding starts at $240. (thanks, FierceFish)