Above $40? You'll probably need to get something above $40. I'm really suprised it's stable with that $300.

I suppose you could try to get something cheaper on eBay or the Anantech forums. Even then, you'll want something around 500W (480-520) and it can't just be any PSU. It has to be from a good company. A few examples are Fortron, Enermax, OCZ, and Antec. If you look hard enough, you can probably find a 480W from one of those companies on either site.