here are other, cheaper, humane methods that are quick and painless. Also, what are we paying executors so damn much for?
The reason capital punishment is more expensive than life imprisonment is not executor pay, rather the insaneextra legal costs that is neccesary due to the sentence being irreversible. This means that it's quite hard to make executions cost effective compared to life imprisonment unless you believe the reduced costs makes up for the increase in executions of innocents.
If you want to cut costs, have them work, preferably somewhere where they can get a decent job after release, as a bonus, it makes re-offending far less likely.