I like to match the price of my poke'mon OC customs for one-offs or other closed species customs, with an additional quality option that mimics the style I make fumis in! Here are the prices
$40 usd - messy sketch
$50 usd - cleaned sketch (pokehybrids are done in both messy and clean quality if you want examples although recent batches have a mix of them, you may need to view older batches that specify the commission quality in the title if you want to compare)
$60 usd - full quality (the quality my fumi customs are created in)
there may or may not be an additional $10 price increase for potentially very complicated designs as well!