As you are asking costs I'll relay what it'd cost to have someone else do it for you.

Prices in AUS$.
A15 -> < $1000
SR20 -> $6000
CA18 -> $6000
CA18DET -> $7000 - $8000.

The A15 requires very few mods. Thus is much cheaper.
Remember, these days expect $50/hr for any mechanical work. A typical conversion can take a week of solid work, even if it's been done before.
So that's at least $2000-$3000 labour.

The engine/gearbox costs range from $900->$2500 depending on combinations. And the electrics/computer can cost some more. The EFI new engines are nice though. But you've gotta love 1200s to
go down this path, because you could buy a newer car with this technology 'already installed'. So it's not justifiable in a money saving sense. All in non-turbo form are road-registerable,
but the SR20DET is not. People are registering them without a turbo and putting them on after the engineer inspection. They are in for ~$2000 in fines after the police pull them over and
run the numbers. It immediately voids the registration. Thus driving an unregistered/uninsured vehicle etc etc.
Police do know what a turbo looks like.

Take it easy,
Chris.

does anyone know what type of cost im looking at to dump an a15 or ca18 or even an sr20 into an
81 datsun 1200 ute?

i just need a rough idea