I've seen the economic argument presented, and I don't get it, either way. When one considers the ridiculous amounts that the government spends on other things, and that this is regarding the decision by a supposedly rational people whether or not to take a human life, why would money be such a big concern?
Such a decision should NEVER be taken lightly, by either side. When people oppose capital punishment, the flippant posture toward the victims never ceases to amaze me. Likewise, the average advocate of the death penalty has a strong tendency to want to speed up the process, oppose appeals, and "let the f*&#er fry." Both make me sick.
I advocate the death penalty, but I don't take it nearly as lightly as some would.
The victims outside the person(s) killed, those whose loved one was taken away, deserve to see justice, they deserve to see the offender's life taken away. I don't see how this is open for argument. Further, how one could NOT be outraged at the taking of innocent life is beyond me, and this is what irks me about those that oppose the death penalty, they also tend not to be too terribly bothered by the crime in the first place.
However, I also don't have much of a problem with the cost of appeals, and a strong need for overwhelming evidence. Thank you DNA testing for making that endeavor easier and more absolute! Overwhelming evidence is paramount to even having a capital punishment system in the first place. If a society lacks a requirement for overwhelming evidence, or ample ability of the accused to fight it, then it also lacks the responsibility to have a capital punishment system. So I don't give a shit about the cost.
Take the time to get it right, and when determined overwhelmingly to have gotten it right, execute.
However, I personally would like to include one additional step. I am not a Christian, nor am I religious at all, but I do agree with one aspect of Hebrew law and culture, and that is the basic idea that one cannot be forgiven unless one is forgiven by the victim. Even when one has been overwhelmingly proven guilty of a horrendous murder, one should be given the opportunity to ask forgiveness of the immediate family of the victim, and if forgiveness is given, then that should at least erase the death penalty, even if the convicted has to serve some debt to society. After all, what is the point of capital punishment but for the victims? I couldn't care less about the arguments of whether or not it is an effective deterrent. Now, realistically, the vast majority of family asked for forgiveness will not give it, and so be it, but if forgiveness by the immediate family is given, what business is it of ours?
That last point is simply a personal feeling, and not intended to be taken as a central premise for or against capital punishment.