Roots of the arts (stats)

This is obviously very saga-dependent, but from my experience magi can easily muster such an abundance of mundane resources that it's very, very rare for them to give up a morsel of magical power because of they lack silver, mundane servants etc.

So.

Magical texts copied imperfectly, because of sloppiness, haste etc.? Maybe if the text was only made accessible once, by a faerie queen, to a young apprentice distracted by her beauty. Maybe if some supernatural doom burdens the author, so that some "accident" befalls each copy of his work ever made. But in "ordinary circumstances"? Inconceivable.

Pearls and eelskin, for 1xp (to each and every new member of the covenant)? A bargain! Throw in topaz and aquamarine, coral and turtleshell, turquoises, emeralds and opals, and it's still a bargain. Now, the skin of a selkie, the comb of a mermaid queen and the horn of a sea unicorn? Ok, that starts to be iffy.