Kelli,
E&O depending on where you are might be referred to as something different here are some other things you can ask your agent about: Quai Tam, Business liability, or Business Malpractice.
Here is the name of a company that will scout out policies and give you a few different ones to choose from. NAPLIA
www.naplia.com They have a special form for medical billing companies as well.
The cost will vary, and you might want to check with your own agent first for potential discounts.
When I was in NJ I paid $1300 a year, I'm paying $1450 a year now and have better coverage (go figure?)
So that's why NAPLIA is good, they will go out and scout the companies and give you a few to choose from.