I'm more interested in the cost per bitcoin provided by the BFL unit.

I figure that value is a "floor" value for bitcoins since prospective miners are willing to pay that much for a bitcoin.  A prospective miner would presumably buy bitcoins instead of running his mining rig if coin value drops below the cost of running the rig.

So, what is the cost of running a mining rig in BTC/$?

This would also allow me to make an intelligent decision regarding turning the garage into a bitcoin mine...