It's impossible to say with certainty, but there is no evidence that the death penalty acts as a deterrent, and there is evidence that the possibility of a capital sentence makes juries less likely to convict. That means that you're more likely to have murderers walking around free, not less, and after rather a shorter period than eight years.
No cost saving. No effect on offending (recidivism amongst freed murderers is low because they tend not to be let out if they're still murderous).
My blood runs cold at the idea of someone having the job of executioner. I would cross the road to avoid them, put it that way, and I'd want their psychopathic tendencies mental health closely and regularly monitored.
I think that the modern distaste for any corporal or capital punishment is part of a better understanding of and respect for body autonomy. When we deprive someone of their liberty we still leave them in control of their own bodies and protect them where possible from physical or sexual assault. We don't beat them; we don't kill them.
China is keen on the death penalty. There are forced terminations there too. It's part of the same mindset, and one that I reject utterly.
On a personal note, I was raped, and given a (medical, not judiciary) death sentence by my rapist. There is nothing I look forward to more than the news of his death. But if his execution were proposed I'd be the one outside Downing Street with the petition protesting against. Because it's utterly and always wrong.