One of the biggest challenges with a creative business is getting paid what you are worth. The root of the problem isn't that the client doesn't have the money and it isn't that the client isn't willing to pay you what you are worth. The root of the problem is how you are charging and how you are creating value in the mind of the client.

First, you must create a business based on value pricing and not hourly pricing. The number one worst way to charge (and most creative businesses are charging this way) is by the hour.
Frankly, it shouldnt matter how long it takes you to solve the clients problems or provide your service, it should matter that the client is getting what he needs and what he wants. If youre creating value and youre giving them value, theyll pay you for that value. They shouldnt be paying you for your time. If youre being paid for your time youre essentially setting the ceiling to how much money you can make because you can only work so many hours.
Therefore, you must determine, specifically what your value is to the customer, not how many hours you will work for that customer.

To do this, ask yourself the following questions:

How do you impact that customer or potential client?
What do you provide to them that will help them and helps solve their problems? How will solving these problems impact the customer? Is it a problem with high impact or low impact?
What is important to the customer? Why is it important to the customer? How important is it?
Have they had experiences working with someone in your type of business before? If so, was it a good or back experience? Why? Exactly what happened?
Why is the client coming to you for this issue?
What is the client's definition of success with this project? Ask him to describe specific ways he will know he made the right choice in hiring you.

By getting the answers to these questions - not guessing what the client will say, but actually getting the client to answer these questions - you will have the information you need to create VALUE in the mind of the client. If they perceive your work to be valuable, they will be thrilled to pay you. If they do not perceive your work to be of value, they won't pay you no matter how low you go on the pricing scale.
It's all in the mind of the client. Get in their head and understand specifically what they want and, even more specifically, why they want it. Once you do that, getting paid what you are worth is a piece of cake!