A problem is that the Post tab displays both 'total' and 'each' deposit costs for stacks. The 'each' value will often be non-integer, but the Coins function used to display it can only handle integers.
Options:
A) Don't display an 'each' value
B) Somehow indicate that the 'each' value is approximate
Current best guess for a formula, where:
faction = 0.15 or 0.75 (home or neutral)
count = stack count
duration = 1, 2 or 4 (for 12/24/48hrs)
vendor = vendor sell price