How does the Ransom calculation work for captured prisoners?

when deciding how much each man ransom cost what factors are considered?

Here are my thoughts on what might make a difference:

1. Whether they are a King or Prince.
2. Unit build cost.
3. Command rating if any.
4. Armour/weapon/Morale/valour upgrades?
5. Is a Noble (has a provincial title or title of office).

I have a superb general stuck in scotland, that I'm probably not going to be able to reinforce before he gets worn down by attrition. I really want to keep this guy and I actually think it might be beneficial for him to get captured and ransomed back to me as he could really use the Captured vice (-1 command, +3 Morale). He's already got plenty of command stars, and is a Field Defense Expert and Skilled Poor Odds Defender, but he's managed to get the Merciless trait as well which gives -2 Morale. i could afford to lose 1 command to get the +3 Morale to compensate......But I'm not sure I can afford the ransom!! He's not Royal thankfully but still, saving him could be very pricey.