Thassa, Deep-Dwelling #71 from Theros Beyond Death is a mythic card that currently sells for about $31.87 ungraded, with graded copies ranging from $25.00 at grade 9 to $41.01 at grade 10. A grade 10 copy sells for around $41.01 vs $31.87 raw. That's a modest premium, so grading only pays off for near-perfect copies.