Emily Berl for The Wall Street Journal
Ninth Circuit Judge Arthur Alarcón, outside federal court in Los Angeles, says he is conflicted about the death penalty now, because of its costs.

Once upon a time, say, 35 years ago, arguments about the death penalty tended to revolve around a host of issues, like whether it deters crime better than lengthy prison terms or whether it’s morally justifiable.

But these days, debates about capital punishment are turning largely on one issue: cost. Opponents of the death penalty are finding some unlikely allies: tough-on-crime types concerned about its price-tag.

This consideration is particularly prominent in California, where a referendum to abolish the death penalty will appear on the ballot in November. Politicians in more conservative states also are taking another look at capital punishment, on cost grounds.

Some death-penalty supporters, meanwhile, agree that costs must be reined in, but they say capital punishment should be fixed instead of abolished.

The conflict comes amid deepening uncertainty over the death penalty, which was reinstated in many states after it was upheld as constitutional by the U.S. Supreme Court in 1976. Since 2007, however, the death penalty has been abolished in five states: Connecticut, Illinois, New Jersey, New Mexico and New York. And public support for capital punishment, while at 61%, is at its lowest level in 39 years, according to a Gallup poll last year, the latest available.

The referendum proposed by a coalition of death-penalty opponents in California would replace the death penalty with a sentence of life without parole for all death-row inmates. The state, which last executed an inmate in 2006, holds nearly a quarter of all death-row inmates nationwide.

Some supporters of the referendum point to a 2011 study co-authored by Arthur Alarcón, a federal appellate judge for the Ninth Circuit in Los Angeles, which found California had spent more than $4 billion on capital punishment since it was reinstated in 1978 — about $308 million for each of the 13 executions since then. The referendum calls for devoting $100 million in budget savings over the next 3½ years to investigations of unsolved rape and murder cases.

But the debate is creeping beyond the borders of “blue” states like California.

In Montana, some conservatives are behind a movement to do away with capital punishment because of cost. And in Utah, a Republican lawmaker recently asked for a fiscal review of how much is being spent on capital cases.

“I don’t have any illusion that either the Utah legislature or the people are ready to overturn the death penalty,” said State Rep. Stephen Handy, who called for the study. “But I want to start the dialogue.”