Most abilities are common across all characters and you can choose to upgrade the ability for all characters at once. This is usually by far the best way to do your upgrades, so it benefits whichever character you need to use for a given mission. Only a few abilities are character specific and these are usually best to upgrade later on.

In these tables, the first number given is the amount needed to upgrade just the character in question. The second number is to upgrade ALL characters.

LEVEL 2
orc bane           5k   8k
fog of war         5k  n/a
strength of stone  5k  15k
orc hewer          1k   3k
final judgement    5k   8k