(CNN) The special election for Georgia's sixth district is on its way to being the single most expensive House race in American history, according to calculations made by Politico .

If all current TV ad reservations are completed, the pricetag for the race between Republican Karen Handel and Democrat Jon Ossoff will be $29.7 million -- eclipsing the $24.4 million spent on TV advertising in the 2012 Florida 18th district race between Rep. Allen West (R) and Patrick Murphy (D), according to stats provided by the Center for Responsive Politics . (In 2016, the most expensive House race was for Speaker Paul Ryan's 1st district, with a cost of $21.3 million .)

That is a massive amount of money to be one of 435 House members. And, if Ossoff wins, to be a member of the minority party no less.

Why the incredibly high pricetag? A confluence of factors:

t: Georgia's sixth district is covered by the Atlanta media market. While not as expensive as the New York City or Washington, D.C. media markets, Atlanta is still an expensive place to buy television ads. ( Atlanta is the 10th biggest media market in the country .) That means that if a candidate or campaign committee or super PAC wants to make a real impression with voters in the district, they are talking about a multi-million dollar investment.

Ossoff's massive fundraising: In the first three months of 2017, Ossoff, a political unknown prior to this year, raked in $8.3 million -- an unheard of sum in a House race. That huge haul was due in large part to the fact that Ossoff became a sort of cause célèbre for liberal donors trying to send a message to President Donald Trump. : In the first three months of 2017, Ossoff, a political unknown prior to this year, raked in $8.3 million -- an unheard of sum in a House race. That huge haul was due in large part to the fact that Ossoff became a sort of cause célèbre for liberal donors trying to send a message to President Donald Trump. Ninety five percent of donors to Ossoff through March 29 came from outside of the state of Georgia

The polls: This is a very close race. Both : This is a very close race. Both public and private polling suggests that it is, as of today, a true tossup. Which means that moving a point or two either way could make a huge difference. The prospect of being the deciding voice in a race with this much national import attracts all sorts of outside spending on both sides of the aisle.

* The calendar: The free-for-all primary -- in which Ossoff and Handel finished one-two -- was on April 18. The one-on-one runoff isn't until June 20. That two-month gap between votes is unusual (runoffs tend to be held closer to the first vote) and allows candidates and national parties to raise and spend vast sums that they wouldn't be able to do in a shorter time frame. It's also worth noting that there simply aren't a whole lot of races happening right now -- meaning that if you want to spend money somewhere, Georgia is the only game in town.

* The stakes: This is probably the most important factor of all. Both national parties see this race as a must-win because of the impact a loss would have on their national message. For Democrats, an Ossoff win -- in a district considered safely Republican for decades -- would provide a major momentum boost and help not only with their fundraising but also with their candidate recruitment for 2018. Republicans see a Handel win as evidence that despite the talk of Trump dragging their candidates down, there's no proof he will.

You combine all of those factors and you get an extremely expensive House race. The most expensive House race ever.