Eudora should be 4 mana with its quest requiring 4 cards. Stepping this repeatedly for 2 mana is scary so increasing the quest requirement would be fair. Alternatively it can stay 6 mana but only require 1 or 2 cards from other classes. But at that point it’s hardly a quest.
Maestra can stay 6 mana but should cheat mana on the hero it discovers. I’d say as big as a 3 mana discount would be good.