after taking business classes for 4 years i can tell you that looking at sunk costs is never what you should do when analyzing a continue vs shut down problem. in your situation you have to look at what you can transfer but forget about the costs that you can't get back believe me no good business does... if you put it back to stock how much you think you could sell it for, then maybe sell some of those mods you took off enought to buy the m3 and transfer the rest on there once you get it.
then buy a damn car charger!!!! plug it into the garage and then you don't have to idle it. when i installed all my systems i had to test and adjust them but didn't wanna suck up exhaust fumes so this is what i used, much better than the alternative