How about you have the option to attack someone in the can for 50 e (twice as much as a normal attack)? The caveat would be you can only use fists and kicks since all your weapons are "confiscated" during jail time.
You can only leave lying and hospitalize.
Players who are in the prison's hospital cannot be busted out of jail but do have access to meds; Players who go to items and attempt to equip weapons can do so, however these do not show up in battle while in jail/prison.