You can cover the rig with some plexiglass to mitigate the dust, lol, jk. If it were me, I wouldn't that much for board that will only run one card. Have you checked newegg?
He wants to buy only from Tigerdirect, since they take bitcoin..
I would go with this:
http://www.tigerdirect.com/applications/SearchTools/item-details.asp?EdpNo=3858040&CatId=7248Would give you 4 slots.. for upgrading to more cards down the road for less than the price you are looking at with the mini ATX motherboard.
If you MUST have a case and want to go cheap then:
http://www.tigerdirect.com/applications/SearchTools/item-details.asp?EdpNo=5401115&CatId=1509You want a case with a side fan to keep the GPU's cool. You can run up to two GPU's in a standard case without much issue if you have a side fan and undervolt the GPU's.