Everyone can agree that pricing is tricky. Here, the method is mostly based on value rather than hours or quantities. You should feel that design services related to strengthening your brand aren't an expense but an investment, so ROI is an important consideration when choosing an agency or designer and discussing pricing. This is an overly simplified formula which is only meant to serve as a guideline for an idea of what range your design budget might be in. 


Assuming that you're able to reasonably assess a ballpark range for what a re-brand or new brand deck might yield in additional revenue over a year, then you can determine what you should be spending on that redesign or brand deck based on percentages. The percentages should range from 10 to 30 percent for a great return on investment (with plenty of room to account for risk). This is also assuming that you've chosen a designer or agency that has expertise, a great track record and understands your business goals. The percentages should relate to the size and reputation of the agency or consultant. Larger, more reputable agencies should be considered at a higher percentage based on the lower risk involved.