2002 grand prix gtp coupe sound system upgrade...?

I just recently decided to upgrade my stock system to a aftermarket. i have two tweeters,two 5 1/4's in front doors, and 2 6x9's in the rear deck. looking into getting all four upgraded as well would like to throw in some 15" subs or maybe 1 18 solo X. any well sound recommendations would be appreciated... my budget is around $1500-2000.