first of all do some research this forum has a lot of info of people doing those swaps in both S30's and S130's
second 500rwhp out of anything is big dollars especially if you are paying someone to build it, remember when thinking of getting more power you need to think can your brakes, diff, tail shaft, body and tires handle it? because whats the point of having power if your car cant handle it and you crash :<
i don't know what the laws and prices are like in your area but something like a VH45 may be some where in between a LSX and a CA18, a VQ30DET out of a maxima +RWD box where i am is a relatively cheap and powerful swap and there seem to be strong engines not to mention light