The problem isn't $ with V-Mart, it's years. The Sox may indeed offer the highest AAV, but I don't see them going to more then 3 guaranteed. Maybe 4, but Theo would probably not find that situation ideal. I think on the open market he is going to get 3-5 year offers. And probably a GM or two blow smoke up his ass about how they see him as a long term catcher and wouldn't move him off the position.
Also there is another issue with V-Mart long term. It's if he really foes have to come out from behind the plate. Yes he plays a decent 1B. But me personally I'm hoping that spot is filled by Agon long term(which is reasonable). If Agon is there, the they wouldn't be able to move V-Mart to 1B. That leaves DH, and although his bat is good, he's not your typical DH. Ideally I'd like to see that spot filled with a big power bat or leave it open so to speak to add flexibility to the line up.
I'd offer him 3 years/40M before he hits the market and see if he bites.