Why we are getting rid of our hourly rate

Without following the Ron Baker links, what is a good scenario for how to calculate and use value pricing?

Is it along these lines? "ABC business needs a custom inventory management solution which also doubles as an e-commerce platform. This will likely generate them X amount of money per year, so we're going to price this solution at Y."

If so, how do you quantify these variables?

note: I have no business degree and am a developer.