California billionaire Tom Steyer has spent more than $18 million so far in his bid to convince Arizonans to support a constitutional mandate that half of all electricity come from renewable sources by 2030.

And that doesn’t even count the nearly $4 million he has put into efforts to oust some Republicans from office, particularly Attorney General Mark Brnovich.

New campaign finance reports show that the fight over Proposition 127 is shaping up to be the most expensive in Arizona history.

It isn’t just what Steyer, through his NextGen Climate Action Committee, has put into getting the measure on the ballot and promoting it.

On the other side of the equation, the parent company of Arizona Public Service, the state’s largest electric utility, has poured $21.8 million into quashing the measure.

APS isn’t alone.

Rural electric cooperatives have put another $417,000 into their own campaign to convince their voters and ratepayers to reject the initiative. And UniSource Energy Corp., parent of Tucson Electric Power, has a separate $50,000 campaign against Proposition 127.

All that eclipses the record set in 2002 when Native American tribes put $21.1 million into a successful initiative campaign to give them the exclusive right to operate casino-style gaming in Arizona in exchange for the state getting a share.

That same election the Colorado River Indian Tribes spent $10.3 million in their failed effort to get voters to adopt a different measure that would have provided for more types of gambling and less revenue sharing with the state. And the horse and dog track owners spent $7.7 million supporting their own proposal which would have allowed them to have slot machines as well.

The massive spending on renewable energy comes as each side hopes to convince voters — and ratepayers in particular — of the financial implications of Proposition 127.

APS in particular is relying on a study it commissioned at Arizona State University. There, economists, working with assumptions provided with the utility, said that by 2030 customers could see up to another $1,900 added to their annual utility bills if the mandate is approved.

Prop 127 supporters got their own report from the National Resource Defense Council which predicts that the lower cost of solar would mean residential bills would go down about $360 a year by 2030.

Renewable energy isn’t the only thing commanding a lot of campaign cash.

The Arizona Association of Realtors and its national organization reported it had built up a fund of $8 million in its support of Proposition 126.

That measure seeks to alter the state constitution to make new sales taxes on services permanently off limits. Proponents, operating under the banner of Citizens for Fair Tax Policy, have run extensive commercials arguing that “politicians are looking for more money” and that, without a constitutional ban, “they’re going to do it by taxing veterinary services, health care, every service they can find.”

A newly formed No on Proposition 126 committee had not collected or spent anything as of the end of the campaign filing period.

The other hot-button issue on the ballot has to date not gathered anywhere near the dollars of the first two.

Save Our Schools has so far spent $426,000 on its bid to get Arizonans to vote “no” on Proposition 305.

This measure is a referendum of 2017 legislation which would expand who is eligible to get vouchers of state dollars to send their children to private and parochial schools.

Until now, those vouchers, formally known as empowerment scholarship accounts, have been limited to students with special needs, foster children, children living on reservations and those attending public schools rated D or F.

The Republican-controlled Legislature voted to remove all those preconditions, a measure signed — and supported — by Gov. Doug Ducey. But in a political compromise, they agreed to cap the number of vouchers at about 30,000 by 2022.

Foes of expansion gathered enough signatures to block the change from taking effect until voters get to ratify or reject it at the ballot this year.

A group called Yes for Ed AZ has spent about $26,000 so far to convince people to vote “yes” and allow the law to take effect. It is being financed largely by the Center for Arizona Policy and the Goldwater Institute.

Much of the money for the Save Our Schools campaign committee comes from a similarly named group set up as a “social welfare” organization which can take individual and corporate donations without disclosing donors.

There was no immediate response to a request for a list of major donors to that organization.

Proposition 306, by comparison with the others, has gathered relatively little publicity — and relatively few dollars.

One provision would bar candidates who get public funding from using those dollars to buy services from political parties. But the potentially more far-reaching part of the measure would subject the rules adopted by the bipartisan Citizens Clean Elections Commission to oversight by the Governor’s Regulatory Review Council. And that panel consists of people appointed by Doug Ducey, who has been a beneficiary of the kind of anonymous donations that the commission has adopted rules to force donors into the open.

Proponents have collected $10,500, most of that from the Arizona Free Enterprise Club, an organization that has provided financial help to elect candidates of its choice but has refused to disclose its donors.

Foes have organized under the name of Arizona Advocacy Network Against the Dark Money Lobbyist Power Grab. They have collected slightly more than $4,900, with more than half of that coming from Tom Collins, the executive director of the Clean Elections Commission.