Hey mate, could probably find the answer using a search, but heres a couple of threads that might help out.
Things to look out for when buying -
http://www.skylinesaustralia.com/forums/in...showtopic=35129
Differences between S1 & S2 -
http://www.skylinesaustralia.com/forums/in...showtopic=17349
To get a feel for an approximate cost of the car, check out heaps of for sale ads, should help out a bit.
Cheers