Remember if you go the RB way, even though the engines are cheap and you want it road reg'd as well, add aonther $800 or so on top of that for engineer's report. Plus the brake upgrade etc.. A good healthy L28 will put out as much if not more than a NA RB25DE; DET is another thing, good power for the $$you throw at it but goes back to certificates you need.
A standard L28 with 240Z carbs (Hitatchi's) and elec ignition will get you around 90Kw at the wheels. Install some triples and a cam, and that should go to around 120~Kw; what a standard RB25DE will get you with aftermarket efi setup and lots of $$$. As with any engine setup Kw=$$$