I saved before talking to (or running the crosshairs over) Grimm each time I leveled (merchant inventories reset then), and reloaded a couple times to get an upgraded body part for my creature, for the next 4 or 5 levels after getting the battle tower. It doesn't help your total gold, but if you still have loot to get rid of you can buy a body part and sell enough to get that gold back.
The traders in the bunker have a fair bit of gold, and once you reach the harbour and High Hall there are additional traders (there is one in Dragon Cliff Castle, as well, but I don't recall how much gold he generally has).
Level 1 of the healing spell could help you conserve potions, though after you get your runners upgraded that will not be as much of an issue.
