Do you take some time to visit your mundane parents in Fengheld? (Assuming they are still alive and living there, of course.)
Living on the road while looking for vis means expenses for yourself and your mundanes (lodging and food mostly). Both Herman and Wolfred have Covenant Upbringing, so they are not used to this and will have to rely on Tristan to secure these for them. From what he tells you, it will cost at least 1 pound of silver per month. Herman probably wouldn't care, as such, except that this is the money he set aside for equiping his lab. It also means that after a season of exploration, the small group will have no money left.