Cast a random Lesson spell without paying its mana color. If that spell has X in its mana cost, X is 3. (As of today, there are 20 lessons. Perhaps look up a list and roll a d20?)
Near Mint - $9.500
Lightly Played - $7.600
Moderately Played - $6.700
Heavily Played - $5.700
Damaged - $4.800
Near Mint Spanish - $9.500
Lightly Played Spanish - $7.600
Moderately Played Spanish - $6.700
Heavily Played Spanish - $5.700
Damaged Spanish - $4.800