you will hear loads of stories on what it will cost, traction problems, weight distribution probs etc etc etc its all BS, you just need to set it up properly. My girlfriends RB26 S14 made 360rwkw and had more traction than when it had the 175rwkw SR20 in it
Depending on what level of build you were looking at i would has it at a guess that using stuff like GTR stock radiator and FMIC you would be looking at about $20k. Of course this will change if you plan on running a twin plate clutch etc
You could also use the 4WD running gear if you had the cash but that would blow the budget right out of the water unless you just hack it to make it fit