Given that ASIC mining runs more like 10 W / GigaHash [1] (not 650W as stated on blockchain.info/stats), we are actually looking at more like ~$150K per day, or $56M per year to run.
At the moment, the value of bitcoin is $7.2B [2], so we can assume that if it scales up to $2T (about the same as M1 of the dollar[3]), then if cost scales linearly, it will cost about $15B per year to run the bitcoin network. That is probably less than it costs to pay the mint, federal reserve, and secret service.
1) http://millybitcoin.com/does-bitcoin-mining-use-a-large-amou... 2) http://www.bitcoincharts.com/bitcoin/ 3) https://www.cia.gov/library/publications/the-world-factbook/...