Inland Marine. It's very affordable and is designed for business that have gear that is used in mobile instances. Policy allows ad on's and take off's of items you have covered. So if you sell you're EF 500mm, you can deduct it from the policy for some savings and then add on the new EF 800mm L that you just purchased!
As with many of the other recomendations here, the premium is based on the value of all the items being covered. All accidental type of incidents and theft, etc. are covered...
+1 I have a policy through these guys as well, except I purchased it through PPA (Professional Photographers of America). Both companies are good to work with. They require anything over $200 I believe to be on the schedule. I pay just under $1.50/$100 of coverage for close to $20k worth of coverage. The coverage is quite extensive too. I could leave my gear in an unlocked car, have the gear stolen & still be covered.
+10 That's what I love about them, very flexible and coverage is fantastic, very extensive indeed in my opinion... same type of rates you're quoting...
5D MK III, EOS M3, 100-400L II, 11-24L, 70-200 2.8L II, 24-70LIS, 17-40L, 16-35 4L, 600 EX-RT, 430EX-RT, 1.4X III, 2.0X III