That setup set me back only about roughly $500

Worth every penny!

I bought the MTX Thunderform from Crutchfield, the sub from a local JL dealer, the amp from a local person off ebay, and then I already had the Alpine HU & RCA cables & wiring.

You can buy the MTX Thunderform (just for the box) off ebay though for cheaper.
The JL sub was only $80 from a local dealer too (you need a VERY shallow depth mount sub for the Thunderform box)