Jennifer Victor tallies spending, using data available on election day:

These totals represent a nearly equal game between the candidates.  However, this may not be a fair comparison. The totals for the individual candidates are money raised, not spent (as of Election Day), and the IE total includes money from the Republican primaries.  Also, money spent by the parties on behalf of their standard bearers are not included here.

Some evidence suggests that the Obama team slightly outspent the Romney team.  But for now, it is safe to conclude that the election was not "bought."