Calling E30 M3 experts. I have a friend who is willing to sell me his E30 M3 for a bargain price. It needs some work, mostly minor odds and ends, but most importantly (and costly) a respray from its current yellow to original white color. Once all that is done is should be a pretty good condition car. The only thing with this particular E30 M3 though is that the car has had the S14 pulled out and swapped with a S50. I know these cars generally go for somewhere around $15-20k currently. If we I were to try to flip this car any idea what it might end up going for with the S50 swap?

Edited to add that I believe it is a US spec S50.