I agree with Stephen. Check with any certifying agencies and professional organizations (e.g. IDEA) that you belong to and compare prices. Although price is a major factor in making your decision, make sure that you check on what exactly is covered under the policy since not all policies are created equal. Be sure that the policy covers the type of service(s) that you provide or intend to provide (for example, not all policies provided coverage for my writing, so I had to shop around before settling on a company).
I hope this helps.