TheMilford wrote:I sold an open one a while ago and the box was OK for $7
These are perfect and sealed.
Waynes World of Books has sealed copies for sale at $39.99. They also have copies in "good" condition with moderate wear to the box for $19.99. If you figure their $19.99 one is in similar condition to the one you sold for $7, it should give you a baseline for comparing the sealed copies.
Nobleknight has sealed copies for $19.99 so that might be more in the ball park. They have used copies for $10 too.