What version software are you running? If 2009 or higher, you can ( with a little modification ) fit a Intel D945GCLF2 in there. You will need different ram (i would get 512mb) for that motherboard, but it does come with a built in cpu/gpu.
I do have a few ASUS K8N-VM boards, some new old stock and some used. I would probably sell new old stock for $150 but you would have to use your cpu and ram. Used ones im not sure if work or not but i would probably sell them for $50.