Darksteel Citadel #238 from Modern Masters 2015 is a common card that currently sells for about $2.05 ungraded and around $4.06 at grade 7. A grade 7 copy sells for around $4.06, about 2× the $2.05 raw price, so high-grade copies are worth grading.
Price by Grade
Recent market prices for graded copies of Darksteel Citadel
Grade
Market Price
vs Raw
7
$4.06
2×
Raw (ungraded)
$2.05
1×
Worth grading? A grade 7 copy sells for around $4.06, about 2× the $2.05 raw price, so high-grade copies are worth grading.