Eath penalty and its affects on the economy

the paper is for the American government class, I would like it to include how did over the years the death penalty affected the economy, what states are keep doing the death penalty. what is the cost for the death penalty procedure. Also, i would like it to include the facts that it is cheaper to keep an inmate in prison for life than to put him/her on a death row. All in all i want it to be on subject, with studies, and examples.