Why don't you "hide" it somewhere for a while and make him think that its gone. Maybe he'll straighten up and you guys can get back to a really cool father and son project. These projects can be tough to get your money out of some times. IMHO
Good Luck with your son. Making a man out of a boy is a full time job!!
I agree. Time would be the true test. See if he straightens out, then either resurrect the project, or sell it. Maybe even have a "mock" buyer comer up to the door now and then to see if it is up for sale.