Each prison should have a nice, deep, beautifully landscaped pond with a wharf. At execution time, the condemnend should be led out on the wharf, affixed with weights and tied to the wharf with a rope. After the appropriate salutations and reading of sentence, they should be tossed in. After an appropriate amount of time, retrieve the body and bury it in a potter's field. No real cost except man hours and intial investment of the the drowning pond and equipmwent, which could be used in perpituity. The execution would be quick and relatively painless.