0 dollars, it allready has a vg30
Anyway, what kind of VG does he want? Vg30et would be the easiest/cheapest swap and could get him to his HP goals.
If you want a vg30dett out of the 2nd gen 300ZX's get ready for your wallet to be raped. I don't even want to think of what the total would be from buying the engine and swapping/fabbing that eninge into a Z31
Would he be doing the work him self? That would save him alot of money that could go towards mods or my latest facination, power tools