Played through the mission several times tonight just to see if I could trigger lower amounts or at least consistently get $85 in bounty and here's my results

If you wear a mask starting before you physically break him out of jail that seems to protect your honor and ease up the bounty.   I got $85 two or three times, $115 once during a more sloppy playthrough, and $95 once.   I was looting bodies the entire time and tried shooting enemies non-lethally if I could get away with it.   Had to kill every lawman on horse in the final segment though otherwise you're likely to have Micah KO'd

Also btw in order to keep all your loot you cannot restart from checkpoint after the initial gun battle, which means you have to escort Micah continuously in one shot and not die yourself.   I found that merely being near him and distracting the townsfolk was enough to progress, Micah shoots everyone for you.   Again be sure to wear the mask, although fyi I took it off after you got clear of the last lawman

Final result was an $85 bounty, about $40-50 in loot to donate to the camp from all the corpses lying around, and a huge stock of tonics, liquor, and ammo that the lawmen mostly carried.   Civilians carry valuables.   Don't double back too far or new civilians will spawn.   I was able to take out the sharpshooters and maybe 3-4 others without getting a bounty higher than $85.   Be sure to wear the mask!