If you're buying these parts from anywhere other than a junkyard... YOU're best bet is to go with AFTERMARKET. Especially if your bodyshop is buying the parts, they normally rape you on prices.
If you are dead set on doing a conversion, don't do a 4 door to a 2 door. It looks the same. Do a celica front end conversion, or something... then again, that's pretty dumb too. (not to rip on anybody that's done it) The aftermarket ones are likely to cost you less, and look better. Pic any 4 door bumper, and get a set of z3 fenders (or at least the lightweight stock looking ones) and then you could list those as a mod, instead of *92-95 stock 2 DOOR FENDERS, etc.
If you are dead set on doing a conversion, don't do a 4 door to a 2 door. It looks the same. Do a celica front end conversion, or something... then again, that's pretty dumb too. (not to rip on anybody that's done it) The aftermarket ones are likely to cost you less, and look better. Pic any 4 door bumper, and get a set of z3 fenders (or at least the lightweight stock looking ones) and then you could list those as a mod, instead of *92-95 stock 2 DOOR FENDERS, etc.