Both will be money pits, the Gt-t will be slightly less in the long run as far as modifications go.
Most skylines come over from Japan with some bolt-on goodies, depending on what exactly has been fitted could also save you some time & money.
The R34 I bought already had a HKS pod Filter, HKS B.O.V (plumb-back), short shifter kit, turbo timer, some decent rays eng. mags, aero bodykit with nismo rear bar & a sunroof which was a bonus. I was able to negotiate it down to a lower price than other equivalent R34's with less or no mods at all, so it pays to haggle & shop around.
Good luck with your search & be sure to post a pic when you do