Welcome to the forum! I'm actually on the opposite side of the country, but I can tell you that a chin implants shouldn't cost you all that much (a few thousand or so). When you think about it, there's not much skill involved other than putting it in (it's not like the surgeon is designing the implant himself!) So I guess you just need to find a great plastic surgeon in Boston that specializes in chin implants and facial procedures.
I don't have any recommendations for your city Boston, sorry!