If you’re paying more than $50 for grading of lower value coins, you’re doing something wrong - using the wrong grading tier, submitting through the wrong dealer, submitting on your own, but not being efficient or other.
Graded coins might be offered at less than it cost to have them graded for reasons such as: The submitter thought the coin would grade higher and sell at a higher price. The submitter had a quantity of coins graded (possibly through bulk grading) and some of them were scores, while others were losers. But the submitter was content to sell all of them, hopefully having made money on the group.