o hai!
If you have the time, tools and money then building an RB30 is really no different to building any other motor. If you want a nice drop in package with a stock motor, either buy a halfcut or sell your NA and buy a GTSt.
o hai again! my motor as it is right now owes me about 4k, and that's to just make the same power as my RB20 was making (albeit a lot earlier). Then start adding in things like GT35R (1.6k), new manifolds, custom pipework etc etc etc
Easily at least a 10k excercise in just parts.
I also do not agree with people who modify cars while thinking about what they'll get for it when they sell it. That isn't the point of modifying cars. You will never EVER make back anywhere near what you spent, but that isn't the point - it's all about YOUR enjoyment. If it's what you like and what you want to do, then do it. Just don't expect to make any of your money back