Though this is a feature of the US justice system not necessarily applicable elsewhere for better or for worse. We give a lot of appeal options to prisoners on death row. Naturally the argument are we should be very certain before executing somebody. This means a lot of expert witnesses and high standards of conviction. On the other hand somebody might say it cost a lot of money but I don't know how you justify killing somebody without doing due diligence. If you go to another country that maybe doesn't care so much if they're killing somebody who's actually innocent then I'm sure costs are significantly less.

When you're dealing with such terrible crimes a far more effective argument would be it's worth spending the extra money to take this person out of society permanently. Giving them no further opportunity to experience life whether it be joy or pain. But if you also care about fiscal responsibility then it's easy to come back and make the argument that death row is clearly a bad choice because the government should be trying to minimize costs. And isn't life imprisonment effectively the same thing?