A few of points based on this thread from my personal experience as a licensed insurance consultant (and no, I can’t sell insurance to anyone, just advise about it.)
Commercial and personal are two main divisions in property & casualty insurance. Different risks, different policies, and different premium. You don’t need to take money to be a business as far as an insurance carrier is concerned.
State Farm is a terrific carrier. I use them for my auto, homeowners and personal umbrella coverage. I have been with them for decades, but I do not use them for my farm coverage. Because they have limited and expensive farm coverage. It’s not a line of business they want.
I carry Commercial General Liability coverage for the boarding, breeding, sales and lesson business. I use a specialty equine carrier for it. I am not sure where the OP was getting rates, but my policy costs about $1900 a year and I do a heck of a lot more than board a single horse. While most carriers have to meet a minimum premium amount, the annual premium should not be particularly high. She also could require her boarder to carry personal equine liability coverage; that’s not very expensive either.
Most importantly, however, is this notion of avoiding possible litigation. There is no way, even with the best risk management protocols that it can be completely avoided. Insurance does not prevent litigation; it just gives you an attorney and funds for a settlement/damage award. You still get the litigation; in fact you have to have litigation to trigger a claim. And litigation takes time even when it is settled. Personally, I pay my premiums knowing that in the unlikely event I am sued, I have a lawyer to handle the case and the funds to pay settlements/damages without touching my personal assets. I never wish litigation on anyone having seen my share of liability claims.
I hope the OP never took a boarder or allowed anyone on her property. She is incredibly risk adverse and nothing good will come from assuming more exposure, particularly when she is not properly covering the exposures she has already.