Ok, I think I see what's going on, maybe. First of all I did both Gnass quests: 1) return the chief's errant son, and 2) so too the priest's scrolls. But, and I assume it's a big but, before doing those quests I bought a just few levels of arcane and nature lore in the party just b/c I'm a crazy person and I can't resist clicking on the skill things when the cost is low: "It only costs a skill point?? Such a deal! Etc." Thus for each of my characters I see a range of prices, all presumably dependent on how many (if few) skill points each has when I turn up to shop. Oops!