Gtm kits run from around 6.5k and up, youll need some supporting mods as well...what gets most people is labor, I work at a shop and I am quite handy, so I do all my own work. If you can do the install yourself with supporting mods(gauges oil cooler etc) You can get it done under the 10k mark assuming you buy a gtm kit- someone is actually selling a used one on the forums for 2k which is almost unbelievable, but hey that will drive the cost down! This is why the evo is so much more suited for hp junkies.
My plan is SC kit , so looking right around 500 whp give or take depending on the tuner and high 300's for tq, turbos are a different animal, will get you that tq into the 400s like snap!
This car is not cheap to mod, but rewarding IMO, I bought my Z used for 26k with 10k miles, so buying new will drive your cost much higher than mine.
check out these links:
https://www.gtmotorsports.com/search...keep_https=yes
https://www.gtmotorsports.com/produc...cat=258&page=1
Forced Induction - Nissan 370Z Forum