The race between Sen. Kay Hagan (D-N.C.) and Republican Thom Tillis in North Carolina could become the most expensive Senate race in history.

For now, that title is held by one of two elections, depending on how you look at it. If you convert spending into 2014 dollars, the most expensive Senate race was in New York in 2000, sending a political novice named Hillary Clinton to a new house in Washington, D.C. If you don't adjust for inflation, it's Scott Brown's loss to now-Sen. Elizabeth Warren (D-Mass.) last year.

If data compiled by the Charlotte Observer is correct, the battle between Hagan and Tillis this year could be the first to pass the inevitable $100 million mark in non-inflation-adjusted dollars. "Money spent or committed in the race is poised to top $103 million," the paper's Jim Morrill writes. Most of that has come from outside groups, leading the Center for Responsive Politics, which tracks campaign spending, to award the North Carolina race the dubious honor of being the contest with the most outside spending in history.

Using data from the CRP and news reports, these appear to be the 20 most expensive Senate races in history. (Looking only at general election contests, we'll note, and using data from here and here.)

At the top is Brown-Warren, which we highlighted last year as the most expensive race. A little farther down you see this year's North Carolina race, notable for the length of that light-green, outside-spending bar. (The Charlotte Observer, remember, included money not yet spent in its estimate.)

At the very bottom is another North Carolina race — the one from 1984, in which Sen. Jesse Helms (R) barely defeated his Democratic challenger. That was the most expensive race in history until Sen. Dianne Feinstein (D) beat Michael Huffington in California in 1994.

That race, according to the Miami Herald, cost about $44 million, thanks to generous self-funding from Huffington (the former husband of now-liberal Arianna). But that was 1994 dollars. In 2014 dollars, it cost about $70.2 million. And indeed, once you adjust the above data into 2014 dollars, the picture shifts considerably.

There's that Clinton/Rick Lazio race, probably the first to cross the $100 million (in 2014 dollars) mark. And the 2012 race in Massachusetts drops to third, behind the 2000 New Jersey contest between Jon Corzine (D) and Bob Franks (R). Corzine, too, put a ton of his own money into the race.

That's the big difference. Candidate funding and self-funding are quickly taking a backseat to outside money. North Carolina may end up usurping Hillary Clinton's title for most expensive race, but it isn't likely to join the upper ranks of the most money spent by the candidates themselves.