I need a little boom in my big truck!

[MegaCabMan]

I have a 2010 Mega with the Alpine system. The mids and highs are fine but I'd really like a little more boom. I know there is a sub in the back somewhere though I've never actually looked for it, I'm told that it's there.

I'd like to do something that will keep everything looking stock, so no boxes or big ass amps. I'd also like to keep the cost under two Benjamins.

Is this doable?