I think the bast advice of all would be spend the same amount of money on a real M3, and if you cannot afford one, you cannot afford the conversion, either, so save your money for a real M3 and suck down your pride in the meantime.
It is not possible to save the money and just convert a low model - an M3 is an M3 for a reason, and its price is set accordingly. Keep in mind it is not only a better engine; it is a stiffer and better suspension; thicker frame/body; better transmission to handle the power; I could go on, but just about everything is upgraded. No to mention the interior, such as the M3 Vader seats, and styling, such as the bumpers and trim.
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