I have an RB25 turbo with a dead turbine side oil seal that I could sell cheap
I also have an RB20 turbo with a slight chip in the turbine
I paid $200 for the RB20 turbo, and $350 for the RB25, but the RB25 had been rebuilt, and obviously not very well since it died pretty quickly.
Considering all the custom work required (manifold, dump, oil/coolant lines, intake/cooler piping) to fit an RB turbo to an SR I wouldn't bother. Get an S14 T28 for a cheap bolt on upgrade.
The RB25 turbo was excellent, but since I was doing the n/a turbo conversion I had to do heaps of custom stuff anyway and it wasn't a problem to modify a manifold and make a custom dump pipe.