Its not cheaper if we kill them cheaper. A beheading or large caliber gunshot is cheap and relatively painless. Medical executions aren't performed out of mercy or to save suffering, they're to sterilize the process so that people are more comfortable with it. So many of them go free after their sentences and just reoffend, which ends up hurting innocent people, anyway.

I could get behind life in prison if it didnt cost the public more than the cheapest execution, didnt make people rich, and didnt result in penal slavery. Find a way and I'm sold. I'm less pro death penalty because of the need to witness punishment in action, although I think that's a valid need for humans to have, and more because it's the best thing for society as a whole.