Too much hazmat and bio waste, same with a single bullet to the back of the head. Hanging... too much infrastructure same with ‘ol sparky, and lethal injection. Even the Spanish garrote chair could fail at a critical moment.
But... there is a form of garroting that’s easy, affordable, and effective. Inquisition style:
Cut off their meals 3 days in advance, water only. Restrain to a stout post, pass a length or sturdy line from neck to the back of the post, tie a proper square knot, stick a pipe through and turn the pipe to take up the slack, and keep turning. Cost effective, green, and meets the “simple works” criteria. Little if any clean up due to the imposed fasting period.
Plus the supplies can reused.