That kind of pricing is a ballpark, after getting a M5 engine, wiring (or standalone) transmission, custom drive shaft, custom mounts, cooling parts, labour etc.
Ask Notjoe what a custom engine swap cost, once you start the $$ adds up. People pay in the range of 4000-6000 for a M3 engine and transmission installed in a e36 and that is a straight swap!
That was a ballpark figure....
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