Pricing varies wildly, as do pricing methods like hourly, per design, whole projects, etc. I think the hardest part is going to be finding a vendor who offers something that is similar enough to what you offer to be useful in comparison.
I think you might have better luck just taking some wild stabs at what you think you might be worth under different circumstances AND finding a few other designers who you think you are similar to with regard to services and pricing. Then compare, but be flexible.
How good are you, and how much do YOU think you are worth? Own your rate!