Save yourself some money and just buy this one that someone recently posted in the "For Sale or Wanted" section of this website:
http://adcache.boattraderonline.com/6/3/4/76260934.htm
Sell the motor off of it, and take the $7000 you saved plus the money from selling the motor and buy yourself a new Yamaha 150.
I'm not a big Mercury fan, although I've never owned one. They don't seem to hold they're value very well for some reason.