it is always cheaper to but one with mods in place, i am currently looking at GTRs and i am looking at ones with mods and then factoring in a rebuild at some stage, there is a lot of farily well modded ones out there for under 25k, then factor in another 8k or so for a rebulid..
if you do the sums on doing it all from scratch i am sure you will find this is a way cheaper option