I've had a couple of businesses, inside and outside, adn that sounds about right for liability insurance. They don't care if it's part time or full time - they're insuring you for full time, because they figure you could go full time and they can't monitor you. I ran into a similar problem with my truck - it was a pickup making 1 or 2 deliveries per day, but I paid the same rate as a larger truck making deliveries 8 hours a day. Once they heard the phrase "delivery in a residential neighborhood", that triggered the rate.
Also, check your state's rules for workman's comp insurance. Here, if I don't need a contractor's license, I can have up to 3 full/part time employees without WC. If I have a contractor's license, or am working on job sites (like new construction) where the contractor requires it, I have to have WC on every employee (I can exempt myself). I had 1 full time and 1 part time employee working on such jobsites, and my WC bill was over $4K per year.
My total for liability, truck, WC and additional insurance we had because I dispensed propane at my store was about $10K per year. Retail store, some outside work, some deliveries and 3 FT/1 PT people including me. Add in homeowner's, liability and fire on the store building we own in our own name, regular car insurance and outrageous health insurance for my wife and I because we weren't big enough to form a group. and a personal umbrella liability policy to cover all the exposure, and my insurance bill was about $25K per year. I closed the retail store, got rid of the propane, cut way back on the emplyees and the business, and got my total bill down to about $15K/year.
I never had a claim. I don't much like insurance companies.