2005 Subaru Forester Alternator

[Harley C]

I just joined this forum, so I don't really know what I'm doing, so bare with me. In my 2005 Subaru Forester 2.5L I have 2 12" subwoofers that has a 1000w amplifier. My friend is getting me 2 15" subs with a 8000W amp, so I know I need a new alternator. The light dim when I press on my breaks even without the subs turned on, so with 2 15's and that much output from the amp, I definitely need a high output amp. But I don't have a whole lot of money to play with, but I guess what I'm trying to ask and figure out is what type of alternator am I looking for? How much would it cost me? And is there any other "upgrades/replacements" that I would have to do? I've read a few things where people have had to change out the wires because the output was so high... Would I have to do that? Even if you don't 100% know, every bit of input from others would help tremendously, thank you!