I have to agree with Magnus, build it yourself. I had a dell and had a mobo failure, they wanted 260.00 for one to fit the Dell, I paid about 100.00 for a much better mobo so decided to build one myself. And I am not a rocket scientist. And it also kind of feels good when you get done putting everything together and push the button and everything works!!!! For the money your going to pay you should be able to build a hell of a computer.
Where they (Dell) get you is they make their architecture to where only their pieces will fit. The one I had was a mirror image to the aftermarket pieces so it would not fit. Take the plunge and build it yourself. Or buy one from someone like Tigerdirect or New Egg. But just dont buy a brand name, buy one that they put together,