I have posted this several times on my Facebook page but never here.
How I do it is what it cost me for supplies and double that price. However, on my ioffer site at http://www.sanditipple.ioffer.com/ I have to include shipping.
This is what I should price my crocheting; but I still go with the above scale. So the double wide afghan I did for Scott would cost $150. (Which we discovered after my mess up fits a queen size bed and is more than double wide.)
It is flexible depending on the pattern style and additional embellishments.
Granny Squares Set of 4 - $15-$30
Plain Hats - $15-$25
Novelty Hats - $25-$50
Baby Afghan - $35-$150+
Adult Afghan - $75-$500+