It's really hard to compete with something like this. Or wait for PacificGeek to put up another 3.4GHz machine. Right now, they have a Dual Xeon 2.8 up. If you think you can put together a system even with scavenging parts, good luck with that. I intend to put a computer together, but I understand it's a losing prospect -- I'm doing it more for the learning experience than anything else. I can't believe I've never put together a computer for myself before. It's funny how when one is spending one's own money, things are different. (I've done it for work before.)
What's dying, the motherboard? Is it just out-of-date/underpowered?
I would monitor some of the deal sites (dealigg, digitaldeals, etc.), either way. I've seen both prefab systems and parts. But none of the sites seem to monitor MicroCenter, so you may have to monitor that one yourself (and if you need anything from them, and don't have one close to you, I have two close to me -- the Beltway/MD one, and the VA one).