You should refer them to a professional photographer that already has the insurance.
Then, go and pay your 300.00 to get your own policy for the next jobs that come up.
Your insurance policy is just another part of doing business just like taxes & equipment repairs/rentals.
Pretty much all insurance companies do business insurance.
Call them up and make an appointment.
(a few won't insure business who do nudes, if that is part of your business make sure you ask before you cut the check)
I have herd good things about these guys.
Also State Farm & Farmers carry business insurance.