A subject I was reading about recently.
We know California's yearly prison budget, and their yearly prison population. It's pretty easy to figure out an average cost per inmate for each year - currently in the 80,000/year range - but it gets less accurate when you try to average out the cost of keeping one person in prison for 44 years, considering inflation and everything else. For sake of argument, 44 years at today's budget would mean it cost CA taxpayers $3.5 million for Manson's life in prison.
There's a lot less executions, so it's easier to average out what those cost: “Taxpayers have spent more than $4 billion on capital punishment in California since it was reinstated in 1978, or about $308 million for each of the 13 executions” – LA Times (2011)
More importantly, or realistically, no prisoner in US history has been executed on the basis of cost analysis.