See my post below, it costs tens of millions more to execute someone than to keep them alive. As for whether or not solitary or death is more humane, I'm sure if we posed that question to him he'd choose solitary. As for your last question, the point isn't whether he deserves to be treated humanely, it's whether we as a society are the type to execute human beings. The vast vast majority of the civilized world has chosen not to, but America (mostly the South, i.e., Texas and Georgia) continues to.
If you or anybody else is actually interested in this topic, you should read Scott Turow's Ultimate Punishment: A Lawyer's Reflections on Dealing with the Death Penalty. He was appointed by the then governor of Illinois to determine what to do about Illinois' death penalty, and spends the book going through all the justifications and costs of the death penalty (costs, morality, victim's families, etc.). He begins the book and his research pro-death penalty and ends up recommending that the state abolish it.