i just got a Pioneer TS-W25M 10" subwoofer for $5. Unused, NIB.
It says 500w max, 120w nominal. 40hz response.

What amp do I need?
What shape does the box need to be?
Is the a site for figuring the size of the box?

pioneerelectronis.com should tell you the cubic feet needed.

Is that the one that looks like diamond plate? I used to have a set of them.

It sat in the backroom of the store for about a year... It'* not this years model, pioneer isn't releasing info on it.

And uh, it looks just like this years' model. all black with the silver ring and stuff.

Ah, the one'* I had were like 8 years old. Similar part number, though, IIRC.

They used to have an archived products listing that was easy to find.

Oh, I'm an idiot. The sizes arte on the back of the box.

Sealed:
1 cu. ft.

Ported
1.1 cu. ft.
3 * 12 port

bandpass
.6 cu ft each side
3 * 5 port


Which do I need?

I'd go with the sealed 1 CU FT

Okay, I can build that.

What'* a cheap amp and what features am I looking for?

If you have a stock cd player you will want an amp that has HIGH-PASS inputs. If you have an aftermarket cd player with RCA outs, you will need an amp with LOW-PASS inputs. Many amps have both though. You'll also need an amp with a built in low--pass crossover to filter out the high frequencies. You won't need too powerful of an amp, and it can be one channel. I'll look around a bit.

How much are you looking to spend?

make sure you make it easy to remove for auto-x meng!!