Parts are fairly level playing field with alot of brands. only reason some jap stuff is cheaper because they are non genuine and poor quality.
IMO anyway. having owned a tonne of nissans and paying for genuine or well manufactured parts the golf has been cheaper in allot of areas.
Im currently building a Nissan GTi-R and that is by no means cheap for bits (not only because it is semi rare) but parts for my run of the mill EXA turbo are also fairly expensive too..
I think the only way to have cheap jap parts is to get a pre 1980 corolla or something..lol.....but hey, what fun are they :-P