Oklahoma has become the first US state to execute an inmate with drugs commonly used to euthanize animals. Ellen's been advocating this sort of thing for years. She thinks it's likely cheaper than the existing protocol, and just as effective. Hey, man, that's just how she rolls...
You know what else is cheap and effective? A few rounds of .45 to the cranial cavity. It wouldn't be hard to build a contraption that housed three pistols (or even just barrels and hammers so the pistols can't be removed and used in any other way). Rig up a mechanism that has three different people pushing the button so no one knows exactly who was the actual executioner. All three barrels fire, brain is now gone, person is now executed. As long as everything fires (which isn't hard to ensure), there's a 100% success rate.
Total cost of materials once you've built it? Under $3.
Cheap, effective, and...
wait for it...
wait for it...
Bulletproof.