With Californians facing the busiest ballot in more than a decade, big spenders are poised to make it one of the most expensive election battles in state history — already contributing $185 million to fight over everything from sex, drugs and guns to tobacco and taxes.

The money is piling up on behalf of campaigns for 17 statewide ballot measures — the most since March 2000. And when it comes to big backers, Big Pharma is far and away the towering force.

According to figures released Monday by the nonprofit MapLight, drug companies have already poured $70 million into an effort to fight Proposition 61, which would limit the prices state agencies pay for prescription drugs.

That’s 38 percent of all the money so far invested into the various ballot measures through July 7, the Berkeley-based group reported. Some observers are predicting drug company contributions will top $100 million by Election Day.

“This is their bread and butter,” said Barbara O’Connor, director emeritus of Sacramento State’s Institute for the Study of Politics and Media, who expects the industry will invest as much money as its needs to win.

The beneficiary of that drug company money, Californians Against the Misleading Rx Measure, says they got an early start on raising campaign cash. “As the other campaigns start kicking into high gear, they will start raising more,” said Kathy Fairbanks, the no campaign’s spokeswoman.

The AIDS Healthcare Foundation, the measure’s sponsor, has raised about $10 million, according to president Michael Weinstein.

“Maybe $100 million can convince people to vote against what is in their own best interest,” said Weinstein. “From our point of view, today, tomorrow or 10 years from now, justice will prevail on drug pricing.”

Big Pharma is closing in on the $94 million raised in 2006 — the most by any one side in a single California ballot measure campaign since 2001 — to fight Proposition 87, an alternative energy measure opposed by oil companies, according to Alec Saslow, MapLight’s spokesman.

The nonpartisan group’s review showed unions, school administrators, and the California Association of Hospitals and Health Systems have given $19 million to the campaign for Proposition 55 to extend an income tax increase on people earning more than $250,000 a year.

Meanwhile, Tom Steyer, a San Francisco billionaire and possible Democratic contender for governor in 2018, has contributed $1 million to support Proposition 56. The measure would increase the cigarette tax by $2 per pack.

Other big names in Silicon Valley also have surfaced as preeminent ballot backers, so much so that O’Connor is calling it, “Silicon Valley against the normal political players,” such as labor unions and associations that usually raise campaign war chests.

“It will be interesting if the traditional players can match the funding, and if that funding will produce — or will equal — a win,” O’Connor said. “In this election, who knows?”

To wit: Netflix CEO Reed Hastings, Paul Graham of Y Combinator, and Marc Benioff of Salesforce have given money to support Proposition 62, a measure that would repeal the death penalty and replace it with life in prison without the possibility of parole. The campaign already has raised nearly $4 million.

A competing measure, Proposition 66 is aimed at eliminating delays in carrying out the death penalty by imposing time limits on legal reviews of capital convictions. It has the support of law enforcement groups. Proponents have raised $3.3 million.

Then there’s Napster co-founder Sean Parker, who has contributed about $2.8 million of $7 million total to support Proposition 64, a measure to legalize marijuana.

The committee opposed to legalizing pot, the Coalition for Responsible Drug Policies, sponsored by California Public Safety Institute, has raised $141,000.

A measure requiring actors in adult films to wear condoms, Proposition 60, has raised more than $1.6 million from its only financial supporter, the AIDS Healthcare Foundation.

“People like Tom Steyer and Reed Hastings have already written large checks,” said Melissa Michelson, professor of political science at Menlo College. “I think this is the tip of the iceberg and we’ll see massive amounts of spending.”

But Michelson believes many of the measures are tied to core values “and glossy mailers are probably not going to change your mind,” on something like gun rights or the death penalty.

“I think Californians are used to the idea that some of these initiatives attract a huge amount of spending,” she said. “But what I don’t think a lot of people know is that so much depends on whether you can sow doubt into voters’ minds. Then, the safe thing to do is vote no.”

Contact Tracy Seipel at 408-920-5343. Follow her at Twitter.com/taseipel.