The cost of RV insurance can vary from state to state and from Insurance Company to Insurance Company.
On average some people who pay for full coverage RV insurance spend around $200.00 per month which is $2,400.00 per year.
If you can get your RV insurance bundled with your regular auto insurance then you might get the RV insurance for as low as $100.00 to $50.00 per month.
If the RV is a used older RV then the RV insurance will usually be much cheaper.
I had an older RV and had bundled just the liability RV insurance with my auto insurance and only paid $50.00 per month for my RV insurance.
Of course full coverage RV auto insurance would be around $100.00 or more per month.