From what I've read, the cost of executing a prisoner is greater than senting to life once you include all aspects of conviction. I got this stuff from Amnesty Internationals website, which are several surveys done about execution:
A 2003 legislative audit in Kansas found that the estimated cost of a death penalty case was 70% more than the cost of a comparable non-death penalty case. Death penalty case costs were counted through to execution (median cost $1.26 million). Non-death penalty case costs were counted through to the end of incarceration (median cost $740,000).
(December 2003 Survey by the Kansas Legislative Post Audit)
The estimated costs for the death penalty in New York since 1995 (when it was reinstated): $160 million, or approximately $23 million for each person sentenced to death. To date, no executions have been carried out.
(The Times Union, Sept. 22, 2003)
In Tennessee, death penalty trials cost an average of 48% more than the average cost of trials in which prosecutors seek life imprisonment.
(2004 Report from Tennessee Comptroller of the Treasury Office of Research)
As for personal opion, I'm split on the issue. Capital punishment was originally a public engagement for everyone to see because it was believed that seeing an execution would act as a deterrant to would be criminals. However, if you look at England from the middle-to-modern ages, the system was quite flawed. While executions did happen semi-regularly, there was actually a line of leniency towards convicted criminals, and executions were rarely done when compared to the amount of crimes that were deemed capital punishments. The term "the bloody code" referred to England's law system which had over 200 laws all deemed to be capital offences punishable by death (the majority of them were added after the British Revolution). But to cut a long history short, since the law WAS so strict about death penalties, the judges themselves were more leniant in their rulings.
The major switch with death penalties came in the mid to late 1700's, when reformers saw that public executions weren't working as deterrants, and execution grounds became bawdy houses, rampant with pick-pocketing, cursing, prostitution, gambling, etc, and there was little attention paid to the fact that a man was about to be sent to Heaven or Hell. Due to reformist attitudes (and due to the Enlightenment) more emphasis was placed on rehabilitation, and state executions were moved to inside prison walls, where the crowd couldn't watch (they believed that knowing someone had been executed produced the same effect as having watched it). And pretty much that's where we've been left off today. A mixture between rehabilitation, and private executions.
I honestly don't believe in the death penalty, though there are times when I think they should just take the guy out to a field and shoot him. I think one of the problems with jails is that human rights groups have moved in and complain that the jails are too harsh and whatnot. In my opinion, I think jails should simply be a concrete cell, with crappy food. If you know you're going to have a crappy time in jail, you're not gonna want to go back. But right now, jails are so leniant....(one of the jails around here has a little golf-course)...you get tv, you get exercise, reading material, good food...it's pretty much a camp paid for by the public. Let them sit in a concrete cell, and soon enough they'll either wanna commit suicide, or never go back there again.
Death penalties are done through such a bureaucratic system that it's not really worth it. The only way people know the person has been put to death is through the newspaper, so the only immediate effect it has is on the family. A couple million dollars has been wasted just so that maybe a handful of people care that he's dead. Of course, then you look at China, which has one of the highest execution rates, and they charge the family for the bullet in the back of their sons head....and you think "wow....that's insanely harsh." but if it was a deterrant, then technically China's execution rates shouldn't be so high, because they've been executing people for a loooong time.
I guess to finish this post, it's sort of a "damned-if-you-do, damned-if-you-don't" problem with execution. I guess if I had to put my foot down, I'd have to say no, but some cases make you really think about switching...