230 grain .45 ACP slug to cerebral cortex:
cheaper, quicker and any pain ain't gonna last for long.
Of course it would be better if televised and carried out within 30 seconds of the verdict being rendered.
Once again, does not always kill, does not always cause painless death, often requires the person bleed out before death occurs, disperse lead into the environment, causes massive blood spatter (many convicts carry aids), etc.