This is likely already the case. I haven't found the reference, but I've heard the number 10 million USD as the cost to brute force a message (I think that covers co-opting an awful lot of supercomputing time for a while).

For comparison, but by no means state-of-the-art, there's Deep Crack, which I thought was a neat did searching for a cost: http://en.wikipedia.org/wiki/EFF_DES_cracker