How large and successful the company is somewhat determines how much you can get paid.
I currently work as a Communications Director for a start-up company making only $28,000/year. The title is impressive but the position could just as well be called a "Public Relations Coordinator".
I am currently looking for a new position at a larger company-- at places like a college, government or corporate entity. One marketing coordinator job I am interviewing for at a local college pays minimum $40,000. I have 3-5 years of experience and I think $40,000-$50,000 with this type of experience is adequate pay.
Potential in this field with the right education, the right experience, and right size, successful company is enormous. If you have over 10 years experience, the right skills, with maybe a masters degree, you are looking at getting paid at least $80,000-$100,000/year. Essentially you would have a more important title such as Director, Vice President or President.
I would recommend getting involved in your local Public Relations Society of America chapter, this will help you network, keep abreast of the industry's latest trends, take classes to learn more, and have access to more jobs to apply for.