The problem is my budget. I absolutely need to keep my sub/amp/wiring below $200 total. The good thing is that (after exhaustive homework) that I'm going with an 8" downfiring in a box sitting on the floor directly behind my center console in the 4Runner. It'll be a .5cuft square that straddles the driveshaft tunnel... pretty straightforward. The amp will be in the back in a side console.

I've registered and searched at every ******* car audio forum and searched every thread in every forum with the word BUDGET in the title... and this is what I've decided on. Should be about $170 shipped for both.
http://cgi.ebay.com/MB-QUART-RWE-202-NEW-8-SUB-300-W-DVC-SUBWOOFER-RWE202-/130395739235?cmd=ViewItem&pt=Car_Subwoofers_Enclos ures&hash=item1e5c311463
http://www.woofersetc.com/p6418/Di30...-Amplifier.htm

I've already got MBQuart 6.5" components and coaxials in the doors, so I'm keeping with the theme... and due to the wife, getting an amp with a bass **** mounted somewhere she can reach is mandatory. Both of these units get great remarks for a clean budget setup that won't **** off the neighbors, but will impress the **** out of people used to "premium" OEM systems. I'll have a local shop fab me up a box and I already have some of the wiring... so it'll be like $225, but to go cheaper, I'd be buying Boss or Pyle stuff. I'll keep y'all updated.

 

Are you into SPL or SQ?

 

needs more parts-express.com and talking to y8s.

 

I know what I've bought. I was leaning towards a Alpine TypeR 10" and a Cadence 500watt amp in a wedge in the cargo area, but it would have been another $100+ when finished. Plus I like the stealth aspect... nobody would suspect to look between the baby seats for a sub. The floor is always covered with toys and stuff anyways... and it'll just be sitting there for easy removal. I'm also going to Y the speaker lines and run a second set to the cargo area if I ever transport 5 people and need the feet-room in the rear seats.

This setup is just to generiously fill out the bottom end for a better-than-stock setup. I'm a fan of quality over quantity if it really counts.

Brain, Dayton Quattros from PE also came highly recommended for a budget build, especially for SQ. I've DIY'd 2 home subs with Dayton stuff... but I like the idea of having all the speaks from the same brand, and the deal on the MB's is really good.

Other 8" sub-$100 subs considered:
Boston G2
Image Dynamics
Cadence
RE Audio