Class A Insurance

There are some companies that will write the insurance when you do not use it full-time, and others that offer full-timers coverage. Make sure you purchase what you need. It is true, the older the motorhome, the less the premium will be for comprehensive and collision coverages. The liability coverage, any medical, etc should be the same no matter the year. It may however increase based on the weight of the motorhome. The bigger, the more damage it can cause. We have our full-timers policy with Progressive. Before we went full-time, we had State Farm who does not write full-timers policies.
The state/area where you are purchasing the insurance, your personal credit history, your driving record all play a role in the rate you receive. It is very hard to compare yours to someone else's because of the personal difference in the above.

progressive just quoted me $1250 for a year of full time insurance for my 2001 Beaver Contessa, 40' DP. 500 deductible

I use Auto- Owners Insurance. Not expensive and very good service.

Just for comparison I too am shopping for insurance for a new Class A Diesel Pusher Entegra MH. I've called my current two companies.

State Farm wants $5,500.00 a year
Progressive wants $3,700.00 a year

Both with $1,000.00 deductables and $0 deductable on glass replacement.

Progressive also has their deminishing deductable plan so for every year you go without making a claim they reduce your deductable until it reaches $0 on a claim. Progressive has been very good to me as I had 3 claims in 2017. One for my truck that cost $4,500.00 to fix and a new windshield after a trip to Alaska in 2016 and a blown out driver door window when a rock came off a cliff in Oregon and blew glass cubes all over the interior of the crew cab. VERY LOUD. Freaked our German Shephard out. Dog was shaking like a leaf and he was in the back seat.

We bought a 10 year old MH and our ins agent said the older it gets the less it's worth and the less the ins cost.