$45 per GH/s. If of course your'e doing it as a hobbyist, an idealist or a believer this is the next big thing forever, measuring what you would pay in BTC or USD is irrelevant. If paying for things and having an actual operating market that involves currency that has value is something you're interested, measuring it in USD or a local currency is pretty important at this point.
1 gh/s will only net about .45 bitcoins a month at the current difficulty (that will change fast) - there would be no net profit - it would be easier to simply buy btc for USD. The value of mining comes in the residuals after the equipment has paid for itself