autozone sells remanufactures OEM alts, easy as hell to install, although I've had problems with my autozone alts on my Supra but they have lifetime warranty. I've replaced mine 3 times in the last 1.5 years......I can do it in about 10 minutes now LOL
I think mk3 ones and mk4 ones are the same, but I'm not 100% sure though. They usually have regular ones and "upgraded" ones(higher output). Between $100-$250 I guess, I got a hook up so I dont know real prices.