The 2014 midterm election will be the most expensive one ever

How much does it cost to win a Senate majority in a nonpresidential-year election?

About enough to pay for approximately three-and-a-half seasons of the current New York Yankees roster — almost $700 million — and that’s just for the top 10 most expensive Senate races.

A slew of legal decisions over the past four years that loosened restrictions on outside group campaign contributions has opened the spending floodgates. Through Nov. 1, outside groups had spent more than $498.7 million on Senate races and $283.1 million on House races, according to data compiled by the Center for Responsive Politics.

As the election season comes to a close, Yahoo News looked through campaign spending records, with the help of CRP data, to take a closer look at 2014’s most expensive races.

Of the top five largest super PAC spenders – outside groups that can engage in unlimited, independent campaign spending — three were Republican-leaning and two backed Democrats.

The Democratic Senate and House Majority PACs, run by allies of Senate Majority Leader Harry Reid of Nevada and House Minority Leader Nancy Pelosi of California, have spent more than any other groups — $47.4 million and $29.5 million, respectively. The Karl Rove-led group American Crossroads spent the most on the GOP side — $21.7 million — followed by the conservative Freedom Partners Action Fund and the Ending Spending Action Fund, which have spent $21.5 billion and $21.3 million.

The 10 most expensive state contests through Nov. 1:

1. North Carolina Senate      Total cost: $113,409,103

In North Carolina, outside groups have spent more than $81 million and the candidates themselves have spent in excess of $32.39 million through Nov. 1.

More than $42 million has been spent by outside groups in support of incumbent Democrat Kay Hagan and/or against Republican Thom Tillis. More money has been spent by these groups against Tillis — approximately $35.6 million — than against any other Senate candidate.

Through the last Federal Election Commission disclosure by candidates on Oct. 15, Hagan had raised $22,945,496 and spent $21,989,527, leaving her $980,155 on hand. Tillis had raised $9,055,347 and spent $7,925,168, leaving him $1,130,179.

2. Colorado Senate  Total cost: $96,835,541

In Colorado’s close Senate race, outside groups poured in more than $68.9 million through Nov. 1 in an attempt to capture the seat held by incumbent Democrat Mark Udall.

Outside groups have spent more than $30 million so far against Cory Gardner, which makes him the second-most targeted Senate candidate this election year, behind Tillis.

Both Colorado campaigns developed formidable fundraising operations, according to their Oct. 15 FEC disclosures. Udall had raised $18,323,855 and spent $17,864,959, giving him $536,332 in the bank through mid-October. Gardner, who got a late start in the race, made up his fundraising gap late in the election, raising $10,622,587 and spending $9,212,759 — much of it over the past six months. He had $1,875,029 in the bank at his last disclosure.

3. Iowa Senate   Total $85,079,887

In the bid to replace retiring, longtime Democratic Sen. Tom Harkin, Democrats and Republicans have funneled a huge amount of cash into the state to prop up their candidates, who over the course of the election, have revealed themselves tohave serious political flaws.

Outside groups spent more than $61.6 million in the Hawkeye State through Nov. 1, with $24.5 million being spent against Republican candidate Joni Ernst. This makes her the third-most targeted candidate by outside groups, behind Tillis and Gardner.

According to her Oct. 15 FEC disclosure, Ernst had raised $9,949,714 and spent $7,705,347. The Democrat in the race, Rep. Bruce Braley, had raised $10,803,793 while spending $10,096,491.

4. Kentucky Senate   Total $78,200,173

Kentucky is one of two states in the top five most expensive Senate races where the candidates’ campaigns actually outspent the outside groups. The Bluegrass State has been among the most watched of this cycle, because of the presence of incumbent Republican Mitch McConnell, who is in position to become Senate majority leader if the GOP wins back the chamber.

McConnell, who traditionally raises and spends his own money in his re-election bids, raised $27,956,687 — which is more than any other candidate this cycle. He has spent $25,056,485, leaving him $2,738,176 through his last disclosure in October. 

His opponent, Democrat Alison Lundergan Grimes, built a national fundraising operation that is no joke, either. She raised $17,487,650 — more than any other Senate challenger — and spent $15,279,548, giving her more than $2.2 million in the bank as of mid-October.

5. Georgia Senate     Total $66,414,822

The Georgia Senate race is already in the top five most expensive races of 2014 and has the potential to move up on the list, as there could be a two-month runoff that stretches the race into 2015.

If neither Democrat Michelle Nunn nor Republican David Perdue wins at least 50 percent of the electorate on Tuesday, the two will face each other again on Jan. 6.

Georgia is another state where the candidates’ campaigns have spent more than outside groups, in part because many political action committees were focused on other races as Nunn pulled closer to Perdue in her bid to take the seat of outgoing Republican Saxby Chambliss.

Outside groups have spent $26.8 million in Georgia. The race joins the Kentucky contest as one of the two in the top 10 where Republican outside groups have spent more attacking the Democrat than vice versa.

According to the most recent disclosures, Nunn raised $14,264,949, spent $13,159,081 and had $1,105,870 left through mid-October. Perdue, a businessman who has, in part, self-funded, raised $11,752,304 and spent $11,082,960, leaving him $669,343 in the bank.

The rest of the top 10:

6.         Arkansas Senate      Total $59,647,157 

7.         Alaska Senate                       Total $58,983,669 

8.         New Hampshire Senate      Total  $50,994,999

9.         Michigan Senate       Total $46,882,926

10.      Louisiana Senate     Total $42,920,060