how much are they charging for HKS GT-RS kits there? it should be reasonable money.
nengun should be able to get it to you for around AUD$2k (bolt in kit). alternatively what about a GT3071 (60mm turbine, 56 trim comp) should be 450hp turbo but some fiddling around with dumps, spacers (maybe) and braided lines. it depends on availability in japan. failing that atpturbo.com seem to be reasonable for prices and delivery.
plus if you can pick up a HKS cast manifold on the cheap as they have a divider you could even buy the split turbine housing to go with it which should spool up even quicker. lots of options out there.
how much is too much to spend?
quick edit: greenline have the GT-RS for 222,500 yen.