Cost per vote:
Based on $750M in campaign donations for Obama (66.9M votes) and $238 (donations) +$84 (public funds) getting 58.3M votes for McCain.
As for the $30M surplus that Obama’s campaign generated, I say let him keep it. I mean personally, not rolling it into the next campaign or anything — if you can win and not use all the money, you should get a performance bonus. Maybe only half — send an email to the 4M people on his donors list and tell them they can get some money back if they apply (or send them all Starbucks gift cards or something), adding up to $15M, and then he keeps the other $15M.
Under my plan, if you lose the election, you don’t get this option. You can’t bag the popular vote and take home a big stack of cash.
Actually, given that taxpayers shelled out $84M for McCain’s losing effort, I think Obama should donate the $30M to the Treasury or FEC or whoever wrote the checks to McCain. Then when he inevitably raises taxes, he can at least say that he’s leading by example.