Prison is inpatient treatment. The pretty good management of the mentally ill, constituting a third of all beds of jails, proves something. Inpatient care can be adequately provided, as it is in most urban jails, for a tenth the cost of hospitalization. The gold plating of inpatient care is to appease oppressive but worthless lawyer driven requirements of accreditation and to prevent second guessing in medmal litigation.
Second, the fact that prohibition of restrictive procedures impairs prison officials less than health care setting officials results in great strides in the reduction of the suicide rate in jails, but not in hospitals.
http://www.ncianet.org/suicideprevention/publications/prisonsuicide.pdf
Some of the same methods can be applied to prison murders and rapes, to markedly reduce them by the same percentage.