Republicans need to pick up six Senate seats in November to win back the majority. Thanks primarily to heavy spending from the Koch brothers-backed Americans For Prosperity, the GOP has been lapping Democrats over the airwaves in many of the states where the majority could be won or lost.

With one notable exception: Alaska.

Sen. Mark Begich (D-Alaska) at Washington Post Live's Energy & the Election breakfast forum at the Democratic National Convention in Charlotte, N.C., in September 2012. (Drea Cunningham for The Washington Post)

Because of the relatively cheap cost of advertising in the sparsely populated state, Democrats have largely kept up with Republicans in the Last Frontier. According to data provided a Democrat tracking the ad buys, total Democratic spending has been about $1.5 million, while the GOP has spent about $1.6 million. Pretty even.

The totals include both candidate spending and third party groups. AFP has been the biggest spender, followed next by a super PAC supporting Sen. Mark Begich (D-Alaska).

In the battle for the majority, a Senate seat is a Senate seat is a Senate seat. That's what makes Alaska so interesting. Like Louisiana, Arkansas and North Carolina — the three other states where Mitt Romney won and a Democratic senator is running for reelection — it's expected to be a competitive race. But it's cheaper in Alaska to stay on the air than it is in those states, making it more difficult for Republican groups — which have been the biggest spenders in the Senate battle so far — to dominate.

AFP has been drowning out Democrats on TV across the map, spending some $30 million on Senate races already. Democratic groups like Senate Majority PAC simply haven't been able to keep up with the torrid spending pace. But in Alaska, they don't have to.

A meaningful week-long ad buy in the Anchorage media market is about $144,000 — much less than in more populous markets in other states.

Of the four states in which Senate Democrats are running and Romney won, North Carolina is the most expensive. There, Sen. Kay Hagan (D-N.C.) has been getting hammered by AFP. It's taken a toll on her poll numbers, which have declined in recent months. Total GOP ad spending has topped $11 million there, according to Democratic estimates, compared to $5.2 million by Democrats.

(Note: Calculating ad spending is not an exact science. The numbers are consistently changing as groups and candidates go on and off the air.)

Louisiana and Arkansas are less expensive than North Carolina. But even there, total Republican ad spending has eclipsed Democratic ad spending so far. Republicans have spent more than $5 million in Arkansas and about $3 million in Louisiana. Democrats have spent about $3 million and $1.5 million there, respectively, according to Democratic estimates. In Louisiana, Sen. Mary Landrieu (D) recently made a hefty spring/summer air time reservation in an apparent response to the flood of GOP ads hitting her.

The bottom line is that the blitz of advertising dollars AFP and other GOP groups have shelled out early in the election cycle is worrying many Democratic strategists. But they're much less worried about a facing a huge disparity Alaska than they are in other states.