Here's the problem with your logic on capital punishment. I live in Connecticut, which has recently repealed the death penalty. Here is the reality: Before it was repealed, when a heinous crime was committed, the defendant was charged with the capital crime. They would be told by the prosecutor the state would seek the death penalty. In some cases, this was enough to get the defendant to plead to a lower crime, with life in prison without possibility of parole as the agreed punishment. This made sure that the perp never again would terrorize the public. And it was cheaper. In other cases, the state would pursue the death penalty because the crime was so particularly heinous. Google "Cheshire CT Murder" and you'll see the case where two career criminals, with an average of 20 felony convictions each, decided to rape and murder a mother and two teenage daughters because they "liked their car" and followed them home. This crime was so infamous, that even though the state had elected a democrat governor with a democrat legislature, they could not pass the repeal as the political backlash would have been too great. They waited until the next year when the defendants had been sentenced to death before repealing the death penalty for NEW capital crimes.
After it has been repealed, here is what has happened. With the death penalty off the table, the state could only seek life in prison without possibility of parole as it's biggest gun. So defendants now plead out to the lesser crimes with 25 year sentences instead, and are now eligible for parole. As such, there is no really good way of getting someone put away for life without bearing the previous cost of the death penalty cases, with their costly trials and endless appeals. So in reality, the state has saved no money, but now puts murders back on the street at some point. And the biggest irony is that existing death row inmates are now petitioning for their sentences to be reduced to life without parole under the equal treatment clauses under the constitution. This is still outstanding, but it is likely they will prevail. And the two murderers in Cheshire? Well, they are not yet a party to that case, as they are having their cases appealed first. Once that is done, and their appeals are denied, they'll attach themselves to this litigation, and I predict that their sentences will be reduced as well.
The fact of the matter is that none of this will save any money. The fact of the matter is that the old system worked well, since Connecticut never actually executed its death row inmates, except in one case where the murderer essentially committed state suicide by demanding his execution, and even then he had to represent himself, as no lawyer wanted to make that case for him. Other than him, Connecticut hadn't actually killed anyone for decades. But heinous criminals were kept behind bars for life, without the possibility of parole boards, early release programs, etc. releasing these monsters back into society.
But we're all better off now, right? Yeah, I agree. Now lets go gun shopping!