the reason no one can give you a clear cut answer is that pretty much everyone gives up after a while.
It'll cost you around $8000 to do the conversion complete on the cheap (providing you know a workshop that won't charge you labour and you do some of the work... and you can get parts cheap too)... it'll cost a lot more if you're just giving money to someone to do it for you.
With the cost of compliance on R32's under SEVS so cheap, and the cost of previously imported 15yr old rattlebox GTR's so low still, it dosen't make any sense to do it.
I've got a GTS4 with a 2530 strapped to the side of the RB20DET, Apexi FMIC, exhaust, intake, AFC and EBC and it goes great for what it is, better than any other R32 GTSt I've ever driven. If I was to upgrade it, I'd just sell it and buy an R33 GTR (around $25,000 landed and complied these days).