There is an ebay auction for Mr. Boston for Vectrex. The bidding is up to $860 already with about six days to go.
The game is complete in the box with the instructions, overlay, inserts, and everything. The seller says there are only two known to exist in complete condition.
What is Mr. Boston Clean Sweep Vectrex
Mr. Boston is a brand of vodka that is still made today.
The liquor company customized the game Clean Sweep with their brand logo on the front cover, the insert, and changed the vacuum cleaner into a top hat inside the game. Mr. Boston then gave some of these cartridges away. The exact number isn't known.
There are said to be anywhere from three to five copies in existence today so the game is very rare and highly collectible. I have never seen a complete Mr. Boston auction so I can't say for sure what the final price will be but it should be several thousand dollars. Hopefully the seller's reserve price is so there is a completed auction.
UPDATE: The game did not sell on ebay because the reserve price was never met, but it did end up selling for $7,200 in a private sale on AtariAge.