$12.7 million.

That's how much Democrat Alex Sink, Republican David Jolly and a slew of outside organizations have spent -- so far -- on Tuesday's special election to replace the late Bill Young (R) in Florida's 13th district, according to calculations by the Center for Public Integrity's Michael Beckel. And, the bulk of that money -- $8.7 million or 68.5 percent -- has been spent not by the candidates but rather by the ever-growing universe of outside organizations on both sides of the aisle.

That's a stunning number -- particularly for a seat that could, no matter who wins tonight, be lost in six months time in the November midterms. It's hard to make apples to apples comparisons for how that spending stacks up against previous races but to get a sense, here are the most expensive House races (when it comes to money raised and spent solely by the candidates) of 2012, according to the Center for Responsive Politics.

Now, a special election in a competitive district -- President Obama won FL-13 by just 5,000 votes in 2012 -- in a swing state doesn't come along all that often. And, since the special election is the only game in town for national groups seeking to flex political muscle or test messages for the fall, it gets an awful lot of attention -- from the party committees, donors and the media.

But, the fact that we are talking about spending that is likely to end up north of $13 million for a single House race is still eye-popping.  And, perhaps even more telling than the sheer cost of a race in a single, tough-to-hold seat is that the money being spent by outside groups has dwarfed the spending by the candidates themselves. This speaks to a broader hobbyhorse of ours: For all the attention paid to super PAC spending at the presidential level, the outside spending by wealthy individuals and groups has the potential to matter much more in Senate and House races. Spending $10 million on an ad campaign in a presidential race is nothing; spend that $10 million in a Senate or, especially, a House race and you immediately become one of the major -- if not the -- major player in the race.

In short: Florida's 13th district race is a sign of things to come.