Argument of fact, the death penalty, is it more expensive than life in prison?

paper must be 4 pages long. argument of fact… the death penalty costs more than life in prison..
must have clear thesis. examines both sides, the death penalty, costs, drugs, burials, etc… as well as life in prison, meals, cloths, etc.. any and all comparisons. But my stance is that the death penalty is far more expensive than life in prison. I need 3 outside sources, that i can bring into class to show the professor, so the sources need to be sources that i can get access to, preferably online, a .org website..
Need to have a mla formated works cited page for the sources.