$60 now
I am just doing it for fun for now, but I am really considering ordering an ASIC miner... 10X the power using 6W instead of 280W... And like I said, you'll NEED them soon
I have seen speculation that the end price once it is 'ready' for mainstream will be about $1000 USD per 1 BTC. Since it is divisible by 8 decimals, you don't even really need to think of it in terms of 'per bitcoin' now that the price is getting up there.