When I started out (officially) in May, I did so through a government program called the summer company program, and in said program, we had business professionals come and talk with us, mentor us, and give us some advice along the way. I will never forget what the first speaker said to us. He walked into the room and said "I don't know what you are charging, but I know it's not enough."
basically, have two numbers in mind:
have a price, and have a backup price. your backup price is a bargaining chip. like a card player, know when to get out, have some leaniance but don't cheap yourself out.