I think the cost is inconsequential.
Not to those of us who are sick and tired of paying bills for creeps like this.
For the evil he did he should suffer captivity for life without access to anything he thinks he has a right to - religious books especially.
Religious books are something he'll have plenty of access to in prison.
What he doesn't deserve is a quick and clean death.
I think he should get what he gave others: a pressure cooker bomb planted at low level about 10-feet away should do the trick. It may not be quick and it may not be clean, but it should give him what he deserves.