How much is a rebuilt 1990 Mercury 60 HP ELPTO worth?

My mechanic convinced me to buy a 1991 Mercury 60 HP long shaft ELPTO for my 24ft pontoon that he had in his shop and wanted to rebuild. He found out it was really a 1990 when he tried to get a rebuilt head but no one rebuilds them anymore. I paid him for parts up front, so he didn't want to back out on the deal. Only the bottom cylinder was badly damaged and he did get a piston from Mercury. After 3 weeks of waiting, he got the head ground down and said it looks great. Then he found a hair-line crack in a valve and needed a few other not-available parts which have taken another couple of weeks to find, plus more and more and more excuses. I'm in Minnesota, so the season ended last week. I agreed to buy the motor way back back on Aug 26th with his estimate that it would take about 1-2 weeks. I still have no motor. Today is October 13 and my boat should be in storage by now. How much should I have paid him for this motor and do I have grounds to demand my money back?