Why is the grading fee so expensive?

"PCGS Walkthrough grading: +$250 (+ wait-time 14 days)

PCGS Regular grading: +$120 (+ wait-time 90 days)"


Walkthrough is $150 plus $10 handling and $27 return shipping which should be $187 totol
Regular is $40 plus $10 handling and $27 return shipping which should be $77 total

I understand charging a small fee for processing, but this seems quite excessive