I'm generally in line with Dana Jean, guido, and Tery on the subject. Which means I do not think I have any kind perfect answer, because the circumstances of each case are different. Since we live in a finite world with limited resources, I would point out some of the costs in a different manner. The time from booking to execution continues to grow. I understand that costs are now $50,000+ per year to house an inmate. If they are there for 20 years (which is getting more common) that is $1,000,000 in expenses (and the longer they stay the more it piles up). Notice the chart on this site.
Is it better to house and feed the innocent hungry, or house and feed killers, many with no remorse for their crime? I have a feeling if budget cuts continue, we, as a society, may have to revist this question with a different perspective. And if not death, is there something more creative as an answer, as sometimes is written about in near future sci-fi books.