My suggestion for a 15k budget would be first. Buy a 00 or an 01. Becuase as you probably know the enhanced secuirty in the key with the chip etc...In my aread when i was searching for cars it was hard to find a modded car and i came over a 97 gsr (too bad i couldnt get it). My advice would be spend as less as you can on a gsr and either boost it...lower it and stuff like that or just do some minor engine upgrades and do the jdm front as well. I dont know what your kind of tastes in cars are but, if you find a good gsr first do your dream of the front end and then work from there like lower it, wheels etc...
Damn i wish i had 15k right now....