I based that on you doing most of the work, it's been a while since I went ECU shopping, there are people in the US now that even offer looms and ECUs for Turbo conversion, so it may be fairly straightforward to do a lot of the work yourself.
ProTunerz have Mega Squirt ECU and loom kits but they are not that cheap once you add shipping and VAT/duty.
https://protunerz.com/collections/p...inated-harness-fusebox?variant=31249889361962
I think you probably need to add a grand onto your estimate to do it properly.
Having a robust fuel system with a forced induction engine is crucial as running lean can kill an engine extremely quickly.
I would imagine OEM 280ZX plenums and fuel rails are pretty scarce and the NA 280ZX plenum is smaller than the 280Z version.
If you use a 280Z plenum, you will be limited to 280 ZXT injectors unless you swap to an aftermarket fuel rail.
Also, the OEM 280Z FPR is vacuum referenced and doesn't have a barb to hold the reference hose in place under boost conditions.
Plus I don't know how the OEM FPR would perform under boost instead of vacuum.
Then you'll need a decent fuel pump like a Bosch 044 or similar.