@bythewell - If you want to be utterly practical about it, then the death penalty should be the better option than life in prison. The only reason it costs so much is because of endless appeals. And those are usually not a matter of proving innocence, but rather proving different levels of guilt and whether those should be punished by death.
If we're purely trying to save the State trouble and money, then a swift death penalty is the way to go. Either that, or they should just abolish it altogether.