Ask Marty what it ended up costing him aswell lol. I don't see the cost benefit. The amount of money that conversion cost him could have had a fully built RB30/26 or RB30/25 with what ever turbo selection you wanted, instead of a 220rwkw stock internal RB26 that ended up letting go.
It all comes down to what work you could do yourself, if you could do everything yourself (engine out, engine in, wiring new loom etc) than it wouldn't be too bad.
Just the cost of the engine, ECU, sump modifications, wiring harness, exhaust modifications, intercooler piping, mod plate etc. I would do the clutch, engine mounts, fuel pump and a couple of other things while i was at it.
It all adds up. All the little things that you don't think of start costing a bit. Trust me on that one.