Your statement needs work. No, in all honesty and all truth: it is not cheaper to keep them alive. The statement above by itself is false and needs more substance to try and prove itself to be true. How much money does it cost to beat someone to death? None. I am not saying to beat them to death, but there are more ways to skin a cat. (Edit: Appeals happen even in life sentences. I felt the need to add this to the front of my post to avoid the skimming confusion. That is all)
The drugs currently used are arterial in their use and can become unreliable due to the perpetrator's health, size, weight, height and a myriad of other factors that cannot be accounted for. However, it is a well known fact that the human body cannot function without it's brain.
A captive bolt pistol is a viable alternative. They cost bordering around $2,000 and destroy the brain of a cow. The captive bolt pistol eliminates the bone and brain matter in our bovine friends and it isn't a secret that cow bone is far denser and resilient than human bone. To claim that the bolt pistol causes severe trauma in the subject before death is very sketchy to say the least; it's death, and they know it comes for them. Of course their heart rates will go up.
Further more, the drugs currently in use are not as effective as initially thought. Recent news has that the poor drugs didn't kill as effectively as they were supposed to (hence this thread). The reason why killing inmates on death row is so expensive (besides appeals. There will always be appeals, even for life sentences. Manson puts one in at least once every year if I remember correctly) the drugs are so expensive because there are only a select few companies that sell them and they are patented and protected so only they can sell and manufacture them (unless I'm thinking of another drug article that is the reason). Anesthesia is also another option, but it has not been explored to a satisfying degree.
Bare hands: free. Murderers don't spend hundreds of thousands of dollars killing people, I assure you. Also, to put the expenditure of the government in perspective here's an article on their poor shopping:
https://www.seattletimes.com/nation-world/pentagon-purchases-millions-in-markups/.
Don't fall victim to what someone else tells you. Don't even believe me. Do the work yourself. Do some research, get involved. Just don't regurgitate to me that stupid, cow-eyed cockameme response: "It costs just as much to keep someone alive as it does to end them". No, not true, and people across the planet prove the statement wrong every day.