You should do at least a month of research befor u take a project on..
Depending on the box and amp you had the 8500s in it could cost 1k or a bit more..
Chances are you need a alternator and some wiring that's gonna cost anywhere from 350 to 600 bucks..
Another 450 for a amp and 600 to 800 for subs/sub..
Just for shits I'll give you a basic rundown on a pretty killer system along with pricing
Aq 2200-450$
aq hdc18- 300$
High output alt-280$
Wiring Kit-120$
Box-200$
Cost to install- 125-150 if you install the alt urself..