I did this in college, but it was not to save money. I had a car box with twin 10s and the amps mounted right on the box. I thought the box looked sweet, I didn't use the car during school year, so I thought "why the hell not?" Plus the box had lights behind the translucent cones that lit up with every bass hit. Now that's ghetto fabulous.

But the power supply cost as much as an amp would have. I don't remember for sure, but it must have needed a 10 or 15 amp supply.