I have always found it a contradiction to argue for “humane” when they are talking executing a person, as if there is a humane way to kill people!
If you are going to execute people, a guillotine works great and it’s cheap. Just keep a file handy to sharpen the blade.
Lethal injection is Not humane. First they paralize you, then they suffocate you, then they give you a heart attack. Your paralized so no one can see you struggle.