Hey chris, Having nearly complete an RB26 conversion in my GTS4, which i think would be alot more staight forward then a RWD car like your.
I can tell you right now, IF you cant afford a GTR, you will not be able to afford this conversion, Unless ofcouse you are doing all the work yourself, then you will save a a few thousand, bu tin my case it was all workshop done.
Yes you can use any Rb26, But while its all apart, You should do everything at once, IE Build motor, fix oil issues. Turbos ect ect.
For a solid set up, you will be looking around the $13k mark, and thats whith some used parts, then labour and consumables ontop of that, There are always little annoying things that pop up, Break and are not through of, Now were talking over 20k + already,
you have no intention of AWD i take it? you will need to get a RWD sump and swap them over.
Dont forget this basics which all add up like, R34 gtr dump pipes, Front pipe, New exhaust?. ECU, PS pump, clutch, catch can, airbox, FMIC, and custom piping