Some studies had claimed that the costs of death penalty are much higher than life without parole (LWOP). But these studies are incomplete.  They excluded some of the savings that death penalty brings.

 "Many opponentspresent, as fact, that the cost of the death penalty is so expensive (at least$2 million per case?), that we must choose life without parole ('LWOP') at acost of $1 million for 50 years. Predictably, these pronouncements may be entirelyfalse. JFA estimates that LWOP cases will cost $1.2 million - $3.6 million morethan equivalent death penalty cases.” Dudley Sharp, Death Penalty ResourcesDirector of Justice For All (JFA).

Executing murders will save innocent lives and money. To insurers and economists, it is common to put value on life. FCC economist Dr. Paul Zimmerman finds that executions result in a huge cost benefit to society. "Specifically, it is estimated that each state execution deterssomewhere between 3 and 25 murders per year (14 being the average). Assumingthat the value of human life is approximately $5 million {i.e. the average ofthe range estimates provided by Viscussi (1993)}, our estimates imply thatsociety avoids losing approximately $70 million per year on average at thecurrent rate of execution all else equal."