Illustration pricing doesn't need to be a nightmare
There are many ways to set illustration prices.
By hour is the one I profoundly hate because it's the most unfair of them all. As your skill grows it's common to make your work more efficiently, you found a process that works for you and you get the result better and quicker. So, as you get more skilled will you charge less? I don't think so.
By style and complexity is less unfair, though it's a bit subjective, but to be honest, they are all subjective. Anyway in this case, you may decide how much detail will go on an illustration and charge based on that.
For those who are starting on the illustration market it can be a pain finding your own pricing method because you're not confident enough or you don't have references at all. Many will choose to price super low either because of low experience or in order to get some paid work, even it it's not enough to pay your own food, unfortunately.
Reference prices exist for each market. The book I show below in the image "Graphic Artists Guild Handbook: Pricing & Ethical Guidelines", 15th Edition has a complete pricing and ethical reference for designers and illustrators.
"Graphic Artists Guild Handbook: Pricing & Ethical Guidelines", 15th Edition, by Artists Guild Graphic.
This was a huge help for me, I analysed the price ranges of the markets I wanted to work to and found my own way of charging. Respecting the ranges results on respecting other artist colleagues too maintaining fair prices and avoiding a down escalation just to find a client desperately.
It covers many areas of illustration, such as web and interactive design, editorial, books, packages, fashion, medical, natural science, technical, 3D, cartooning, animation and a wide variety of markets for surface design. For each, there is a price range to guide you.
This book is very handful either for creators or buyers that may struggle with shrinking budgets. It's a common ground to start a negotiation respecting both parts. I strongly recommend it.
Andreia Melo