The latter is not true, and the former is only marginally so. Even the pro death-penalty surveys of cost I have seen have only managed to “prove” that the cost is lower by falsely compounding inflation on to the cost of prison over 50 years, rather than assessing the cost in real terms (link*). The DP is an exceedingly costly business, and I will try and find a cite that can reasonably be considered unbiased, although I suspect this will be hard. A cursory googling brings up either highly anti- or highly pro-DP sites. I find it telling, however, that the latter are reduced to what is an outright lie in order to make their claim.
Quite besides the truth or otherwise of the cost and convenience claim, I find such arguments to be quite repugnant. It would surely be more convenient if we were to cut off the hands of thieves and let them loose again, less costly if we were to put out the eyes of paedophiles. I do not believe this to be a slippery slope argument; it is a direct consequence of what happens when you let convenience dictate what the state does with people’s lives. This is supposed to be justice, not handy disposal. And speaking of justice…
My personal opposition to the DP is mainly rooted in its finality (although there are many, many other reasons), and this is why I am quite comfortable in my support of LWOP. No court system devised by man is infallible, and innocents are inevitably convicted. How does one revoke a death sentence, once carried out? No doubt the reply will be “well, we’ll only do it for the ones where we’re absolutely certain.” Really? Isn’t that … all of them? We’ve already convicted these people beyond reasonable doubt, and yet somehow 115 have been exonerated since the DP was reinstated, against 927 executed; several of the former were only exonerated after an investigation by journalism students uncovered massive miscarriages of justice. If we have some magical standard of utter certainty that we can bring out in only these cases, why have we not done so? Clearly we aren’t certain, or the exoneration rate would be zero.
Is it sane to put such an absolute measure in the hands of a system which has been proven, time and again, to be so fallible? How can we as humans devise a system so perfect that it can exact the ultimate price from someone?
*Indeed, the “study” in the link provided admits as much, then proceeds to ignore this enormous factor.