Fey creatures do not get their magic from the same sources as Clerics or Mages. In fact their power comes from the Feywylde itself. The magic of the fey is known as the Reverie.  Fey races receive mana points as spell casters do.  If the fey does choose a class with mana then their class mana points will supersede their race mana points when they class.  You will still add in the mana points you have received up to the point to your total mana pool. Fey that take classes can still access fey spells when they reach the appropriate HD/ Class level indicated for each Fey spell level. Mana cost for fey spells are the same as the standard cost for each spell level.