Help me pick out a subwoofer for this amp...

[_paralyzed_]

That's a boston acoustics sub. The only reason it is cheap is because it's discontinued overstock. Boston acoustics is a well known hi end manufacturer.

Other subs are hobby king quality, boston is tekin quality.

A more expensive sub will just require more power and won't be as loud with your cheap amp.

If you want to leave the stock speakers I could probably find a box, a better amp and 2 12" subs for $350 and then you'd really be bumping.