I'm be worried about buying refurbished boards. Anyways, I generally exclusively shop at NewEgg unless theres a steal on another site.
There are three motherboards (new) that would fit your needs. Socket 478, AGP and DDR support. However, they are micro ATX style. They'll still fit in your Midtower case but performance wise they are not going to be the same as a Socket 478 full size board that was still in production in the past. They have onboard video but this is easily disabled.
They run around $40-55 and I'd recommend either the Asus or Biostar, avoid the ECS.
http://www.newegg.com/Product/ProductList.aspx?Submit=ENE&N=2010200280%201070509907%201073407577&bop=And&Order=RATING In all honesty, save your money. Buy a new motherboard/cpu/ram/power supply/video card when you have the money. You could do this for around $300-500 depending on how fast you want it.
Otherwise if you can chug along on your current rig for whatever you need for uses, then by all means replace the motherboard. Just remember that Socket 478 is quite dead and your options are very limited.