Ah, my favorite phrase...
I am sure that BSW wishes they had in stock a stealthed 10" sub enclosure for the right rear corner where the DSP sub would go.
Since they don't, I am going to suggest finding someone that makes fiberglass molded enclosures in your area (a shop, I mean). We usually charge 400-500 for a single-driver fiberglass enclosure and we're in the big city (simply meaning that overheads are lower in Boise than here).
If you got that sub box made, a decent $100-180 10" is fine, and a $250-400 amp is fine, and you can get the whole thing installed for under a kilobuck.
Of course, if you bypassed the OEM amp and used the MBQUart passive crossovers, you would get lots better bass out of the doors than you do now... if you have those passive crossovers, then you might consider getting a 4-channel amp and running the fronts and the sub off of an aftermarket amp.
If you're coming to Portland soon, we can do it
