My Uncle uses BoatU.S. for his sailing craft, and for his powerboat he uses strictly on the Chesapeake. They have low prices and good services, depending on the boat. His BoatU.S. coverage stops as soon as he leaves US territorial waters.
My dad uses National Marine, but he doesn't take his boat out of US territorial waters.
Progressive is cheap, and offers good service, but they're pretty slim on the amenities.
American Boating association is really cheap, but not bog on extras.
You really need to go to their websites and get their free quotes and see what they have to offer you. All their prices are across the board because their services are across the board. You just need to find the right price with the right services.
Insurance companies will often also change their rates for racing crafts, so make sure you make that known when you finally do choose somebody, else you may find yourself SOL at the wrong time.
But, since you're rocking an E-scow, the whole international waters thing likely doesn't apply to you. If it does, you're crazy. Go with Progressive.