rates are going to vary, your market, years in business, fulltime/parttime, type of equipment, amount of coverage, years of experience, things of that nature are going to affect costs. Do you want coverage that will cover you from theft, damage caused to rented equipment, are a few more factors.
Get quotes from multiple agents, have them each quote you for a few different carriers. I had two different agents quote me the same exact policy from the same insurance carrier, one agent was 10% higher than the other.
All that said, you can probably find a simple 1/2 million dollar policy to cover you for damage you cause to a customer's property or injury you cause, for around $500 +-.
Why do people not respect us as they do other tradesmen? Because every Tom, Dick, and Harry doesn't think he can be a plumber or electrician!