For Fun: Cheapest Multi-GPU Rig Possible

So I had a family member offer me some old GPU's (2 GTX 750ti's and a SAPPHIRE R7 360). While I most likely will not use them as I would have to build a new rig to accommodate them, it got me thinking on a fun project/discussion for the forums. Let's see how cheaply we can make a rig to run these three!

I have a few spare parts lying around from my other computer hobbies, such as risers, PSU, hard drive, and maybe some ram, so I guess the focus would be on the MOBO and CPU.

(Yes, I know this isn't going to be hardly profitable if at all. This is purely for fun.)

Look for a used CrossHair Formula 4, it can fit 3 graphicscards. Then you can fit everything in a normal chassie.

On the other hand if you already have raisers, any used mobo for 20$, that fits your ram, and has 3 PCIE x1 slots, would probably do?