John Howard Sanden, founder of the National Portrait Institute and the seminars that gave rise to today's ASOPA and PSA, wrote a book in the '70s called
"Successful Portrait Painting." He devoted an entire section of the book to building a career and includes a helpful chart of suggested prices. Compare that to what you glean from surfing the web to make your own price list. Sanden's book is out of print but you can find copies available through
http://www.amazon.com, http://half.com or Powell Books from time to time.