INDIANAPOLIS — Indiana’s 2012 election cycle has highlighted a truism in politics: Money matters.

Indiana’s gubernatorial races have always been pricey battles, edging above $31 million in combined spending in 2004.

But Indiana’s Senate race joined the governor’s race in the stratosphere this year through a combination of surprising vulnerability from the once-untouchable U.S. Sen. Richard Lugar and new campaign finance rules, fought for by Terre Haute lawyer Jim Bopp, which this year opened a flood of outside spending in even the most marginally competitive races.

At the end of last week, roughly $10 million had been spent on air in the Senate battle. Add in the roughly $6 million spent by Lugar, state Treasurer Richard Mourdock and the many outside groups which fought on either side in the Republican primary and the new spending total hits $16 million.

And the rate of spending is only likely to increase in the final 30 days of the race.

“The races here in Indiana are very much in play and Hoosiers are known for splitting their ballots, so money can be used here effectively to persuade voters,” Jeff Harris, spokesman for the Indiana AFL-CIO, said of the outside spending now pouring into the state.

One of the biggest reasons Democrat Joe Donnelly has kept pace with Mourdock has been the help of Democratic-aligned outside groups who have matched Republican-aligned spending in Indiana almost dollar for dollar.

The heavy spending may be a new dynamic for a Senate contest, but it is de rigueur for governor’s contests.

Republican gubernatorial candidate Mike Pence has been able to run a highly-disciplined campaign with controlled media access largely because he has held such a commanding fundraising lead.

Democratic underdog John Gregg had to ply Statehouse press almost daily for coverage, or “earned media” as the campaign operatives call it, before he began spending heavily on-air.

Pence has been on-air since May, defining himself with light-hearted commercials and has basked in a strong lead in the few public polls taken leading up to the general election. Gregg got on air much later with a series of spots based out of his southern Indiana hometown that both defined him and attacked Pence.

As of the last fundraising tallies, which accounted for money raised through the end of June, Pence had raised close to $10 million and Gregg had collected roughly $4 million.

In the last competitive battle for governor, Gov. Mitch Daniels spent $16.8 million in 2004 to oust former Gov. Joe Kernan, who spent $14.4 million. Hoosiers should know soon whether Pence or Gregg are approaching anywhere near that level of spending, as campaign finance reports for the final quarter before the election come due.

Pence’s fundraising includes some of the biggest names in national conservative circles. Foster Friess, the Wyoming investor who almost singlehandedly bankrolled former U.S. Sen. Rick Santorum’s presidential bid, gave Pence $25,000 last month. David Koch, the oil magnate financing much of the tea party’s efforts nationwide, found $100,000 for Pence at the start of the year and Marriott hotelier Dean White has given a combined $225,000 over the last year.

Gregg’s biggest donations have come, unsurprisingly, from national labor unions. In June, the Midwest Region Laborers’ Political League found $200,000 for him and the embattled Indiana State Teacher’s Association donated $150,000.

And all of that money is needed, as the gubernatorial candidates compete with Mourdock and Donnelly for valuable advertising slots on air and voters’ increasingly scattered attention.

“That’s why that kind of stuff is so important: Who you need to reach in order to win. The ad strategy is penetrating and hitting those people even in the midst of the clutter,” said Indiana Republican Party spokesman Pete Seat, a veteran of U.S. Sen. Dan Coats’ successful 2010 race. “How many folks do pay attention to these ads? And how many come away with positive and negative views?”

To put the on-air clutter in perspective: This Senate battle has seen close to double the amount spent in Coats’ race just two years earlier. And the final 30 days of any campaign are always the priciest.