If you already have the million and this is an extra requirement I'd figure the added cost into your bid or your hourly rate as an additional cost. I've had several jobs where they want "extra's" that are going to price me out of the work, meaning, it ain't worth doing because it will cost me so much in additional insurance for a one time deal. If you plan on doing work with these guys over years and years then eating the cost to keep them smiling is the only alternative.
Make sure you understand, this is NOT your normal, down the road, vehicle liability insurance. This is insurance to cover any damage you and/or your vehicle may do to other vehicles, buildings, the project AT THE JOB SITE .
This is another line on your insurance certs that is included with your Liability Gen Agg, Workers' Comp, etc. I don't remember it really affecting my premium very much. The main cost is the Gen Liab and Worker Comp.
If you look at a copy, which my agent sends me a copy for each company that wants 'Additionally Insured' standing on my policy, you should see the space for that coverage. If it is empy then you don't have it. Call your agent. Don't use your normal vehicular insurance carrier unless they are the same ones carrying your General Liability for your work coverage. Most of them don't understand what that classification actually covers and will charge you too much. At least in my experience.
Have a Great Day, Brent