By way of Mother Jones is this great chart comparing the costs of presidential elections from 1860 to the present:
What’s remarkable is the extent to which election costs are very stable, at least until the last eight years, when they begin to explode. 2012 promises to be an even more expensive election, but I’d be careful before attributing that to Super PACs. Any number of things could be responsible for the change, from the growth of independent groups—which predates Citizens United—to the revolution in small donors we saw during the 2008 campaign. Even without anonymous donors and eccentric billionaires pumping millions into campaigns, it’s possible that we’d still face an extraordinarly expensive campaign season.