I can't blame the op for wanting to do this swap since the IS300 weighs less than the ISF (3,307 LBS vs 3,780 lbs). I'm too am not sure about exactly how much the ISF engine swap would cost but I'm just going to go on a whim and say that it'll be less than 10,000 cr because the LFA V10 engine cost 9,300 cr. Also, keep in mind that despite the fact that you may have 100% off for parts, you still have to pay for conversions and everything else from there on is free.