Car Audio to Home Sound System...LETS DO IT!!

I'm with the others who say you should just get a dedicated home sub. For a little bit more than the money you're going to spend on this, you could get a very nice sub from a company like HSU, Elemental, or Aperion that will shake your house. If you're going to do it, do it the right way.

EDIT: I just read your reasons for doing this, and let me tell you, there is 1 thing worse than no bass - distorted bass (which you'll get with cheap power supplies and this setup). It hurts your ears and makes the music borderline annoying to listen to. Scour craigslist for a used sub. Just because something uses less power does not make it a worse sub. I'd be tempted to say my old HTIB 200W Onkyo 8" sub would sound better than what you're planning. If you were local, I'd sell that to you for $50. You should be able to find similar deals close to you.