Sub: American Bass HD 15 for $225
Amp: AQ2200 for $225
Get double07 to build you a box => roughly $150
Wire for big 3 and batt => $3/ft
Secondary battery => $280
You could probably find someone local to help you with install, or do a lot of research on here to learn how to do it yourself.
You shouldn't need a HO alternator for this setup and should have no problems being louder.