One talkative and charismatic alt can get you out of the jail, always.
So how about that you must be online to get out when someone else is paying/taking you out? Alt problem dissapear.
Will be abused by players who got everything anyway.
Maybe, but finally you will get rid of that and become more carefully next time, 21(lvl)*500caps = 10500caps - that's not so small, even for that 21lvl. Anyway, 500caps per lvl is just example, it may be 1000.
Players who have everything anyway, can always raid the jail. We already have some smaller player groups who can raid whole (guarded) towns.
That's the point, we like it and wants it (maybe not everyone). Raiding prison is a lot better idea than making an army which is stucked in one place and depends from whims of Izual....
Same as above, once you got the skills, you do it in a short time.
Not everyone has enough sneak skill (and/or luck) to get out this way. If he fail, he will get into separated cage from which he wouldn't escape. Then the only way to leave is to wait or have friends who will pay for ya.
And about players without nothing... that's just their problem they hooliganize in guarded city without friends/money/skills/charisma.
And look for players reactions - they like it, I see here a lot more enthusiasm than in the "BIG-UBER-PRO ARMY ROLEPLAY!"...