The pussy Democrats will insist they live life in prison, on our dime. The rope would cost virtually nothing, but nope, let's set them up in house arrest on the taxpayer dime for the rest of their lives.
If cost is your argument, you picked a bad one. The full cost of trying, convicting, and sentencing someone to life in prison is cheaper than the full cost of capital punishment. Significantly cheaper, by a factor of about 2 to 5.
I'm pretty sure you'll argue that it costs so much money to execute someone because of all those pesky pre-trial procedures, elevated trial standards, mandatory appeals, and high-security incarceration of the condemned. Why not just get rid of all that? Well, because the state putting someone to death is a huge deal. It's a sentence for which there is no just remedy if it is arrived at incorrectly. So the state should be held to an exceedingly high standard for such trials, indisputably much higher than for life-in-prison cases.
IMHO, the state shouldn't bother. Don't hang 'em high. Lock 'em up instead.