Insurance will vary by state (with the exception of health insurance under the Affordable Care Act, insurance is generally regulated at the state level). I just went through this in Minnesota; for reference, here are the two options I had :
(1) Cover under homeowner's policy. This has no additional charge but has three very bad limitations :
(a) It only covers persons named on the policy (my wife and I), so no coverage if my brother or friend use the tractor.
(b) It only covers the tractor for use on our property (no coverage in transit or at the neighbors, etc).
(c) Deductible is the same as our homeowners policy. Particularly bad as we chose a high deductible plan for the house.
(2) Separate policy. This covers the unit anywhere with any user authorized by me for non-commercial use. Commercial use policies are available but more expensive as they generally assume higher use, less skilled employees, and include some degree of liability insurance.
I chose option (2) on a 3720 I purchased. $250 per year with $500 deductible or $365 per year with no deductible, $27k coverage. I think the cheaper plan has a no deductible for the cab glass, but I'm not sure as I chose the no deductible plan since this is a new unit for me to get used to. This covers any damage to the tractor, loader, or mower beyond normal wear. For example, if the tires go bald, it's my cost. If I hit an obstacle and tear out the sidewall, it's covered.
I got this through State Farm of Minnesota. I didn't have a chance to shop around as I bought it at relatively short notice in Iowa and wanted to get it covered for the trailer ride home! I hope these points of comparison help you in your decision.
I will probably shop around a bit a year from now, but my local agent is a good person to deal with. Prior threads I have read on the subject of tractor insurance have often described trouble actually getting things covered. All I can say is that when I hit a deer one night, I emailed my agent and woke up to an email from her authorizing the full repair, no problems. My friend hit a deer and his insurance company tried to not cover it because he didn't have a police report...
Peter