Upkeep is generally half muster cost - or a 1/4 is garrisoned. My favorite goblin unit was goblin rabble which had 1/4 GB maintenance (they were, admittedly, cannon fodder with terrible morale and discipline by any standard).

BRCS.
Infantry: 1 GB muster, 0.5 GB maint, .25 GB garrison
Archers:1 GB muster, 0.5 GB maint, .25 GB garrison
Guard: 3 GB muster, 1.5 GB maint, .75 GB garrison
Wolf-riders: 4 GB, 2 GB active maint, 1 GB garrison

Thurazor has 19 province levels and say 6 (a third, alamian sort of level) law levels giving the king so 21 GB regular income, the guilders probably chuck in the odd GB to keep the goblins sweet, while the temples probably cast the odd beneficial realm spell, agitate, or send some units to support the king.

Assume a L3 court, 4-5 GB for actions/spending, and you get military maintenance of, say, 11 GB per turn.

1 wolf-rider, the king's own - 1 GB
2 guards - 1.5 GB
12 archers - 3 GB
12 Infantry - 3 GB
4 scouts - say 2 GB

Of course when Thurazor goes to war that army gets twice as expensive, so the goblins better either have built up a treasury, or start pillaging quickly. That said, given that the king probably leads any army, the court cost will drop to 1, and actions will also be reduced to 1-2 GB, so if need be the goblins should be able to stay active for a while even on a low treasury.