I think Missi sums up nicely the feelings you get when deciding what to charge. I sometimes think I am being presumptuous and taking advantage of a desperate situation to charge the fees that I do. I have learned I am very low priced for the market in my area. And I do not have to work for them, so I can charge to make it worth my time. The next time I get a request for STG's services, I will be re-printing my fliers and raising my rates.
Guilt is a big factor when deciding what to price.
However, if you know in your heart you are providing the type of service or product that can't be found on every street corner and you are being pursued because of your skills, don't forget to add all of your costs into your rates. You'll feel so much better about yourself and you'll make more money.