I'd say skyline prices, or any rwd car(e36's,mx5's,recommended drift cars) prices have went up in the last couple years is a lot to do with the demand. They're sought after more and more as everyone wants to drift. even vw clean freaks are jumping on the band wagon.
your r33 auto is probably gonna cost you around 3000 minimum to build once you find a car,motor,box and conversion parts but then you've got brakes to consider along with some sort of suspension,seat,harness,wheel..... the list goes on. you may find your better off trying to find a 33 gtst around the lower end of the scale at 3500 with some mods and taking it from there.