Not according to those that already have the death penalty it isn't. Read and weep you sick puppy...
"...In the 32 states in the Union where the death penalty is legal, as well as the federal government, the death penalty has grown to be much more expensive than life imprisonment, whether with or without parole. This greater cost comes from more expensive living conditions, a much more extensive legal process, and increasing resistance to the death penalty from chemical manufacturers overseas. These costs could even become higher, pending the outcome of various lawsuits against various states for their “botched” executions. Each death penalty inmate is approximately $1.12 million (2015 USD) more than a general population inmate...."