Value of Value-Based Pricing: Should a Creative Professional Charge on an Hourly Basis, or a Project Basis? Here's the Answer
http://www.creativelatitude.com/articles/articles_stuart_value.html

Stuart, Valarie Martin
Creative Latitude
2004

Abstract:

We creative professionals tend to be a right-brained bunch, harnessing our creative talents to create practical solutions for our clients. Creating pricing structures, estimates and invoices are not high on our enjoyment list. But we can avoid some common pitfalls and potentially unhappy clients by pricing our work based on project value rather than an hourly rate.