I was able to buy my level 20 Fury spell at the top of the tree in Elddar. Its a scribe inside the tree house that sells them. My Guild friends (2 Wizards) bought their familiar spells there and I don't believe they go for 50s. These are fun spells that don't really do much to make you more powerful.
My fun spell is Faerie Fire which surrounds the enemy in green fire. Its costs no POW, has a long recast timer and does nothing else.