I also have an Inland Marine policy, through Farm Bureau Insurance.
I honestly couldn't tell you what it costs, because they also have our home and cars, and our Rep gave me a package deal.
The reason an Inland Marine policy is important is that most "tractor" or homeowners policies do not cover you when you're off your property. The Inland Marine policy covers you when you're, say, trailering it to the shop for warranty work, helping the neighbor across the road right the skid steer he flipped, or, in my case, driving on my state-maintained dead-end road the 700 yards it takes to get to my bottom barn and pasture.
State Farm had all my policies until I bought the tractor. I asked, specifically because of advice I got on here, for an Inland Marine policy, and they just wanted to keep arguing with me that it wasn't a boat.
I walked into Farm Bureau and told them I needed to insure a new tractor, and they said "now, this is going to sound crazy, but what you really need is an Inland Marine policy. Let me show you what we got." An hour later, they had all my policies.