Extended warranty prices vary widely, depending on the terms of the policy (coverage), the type of powertrain (diesel vs gas), age of the RV, amount of the deductible and the fees paid to the seller. Trailers are far less expensive than motorhomes, because of the lack of a powertrain. Diesels are much more expensive to insure (high cost of repair); older rigs require more repairs and are out of all manufacturer warranties; RV dealers get large commissions for selling extended warranties (but prices are sometimes negotiable). You can get basic coverage on drive train and major appliances for much less than a policy that covers everything, e.g. electronics, awnings, etc.
When we bought the 04 Tradition, I was quoted over $5000 by a dealer for 5 years of broad coverage. Good Sam wanted $1600/year. The policy I bought thru Warranty Experts had slightly greater coverage for $3200. The 5 year policy on my 02 Dolphin (gas) was only $860, but I got a steep promotional discount on that - it would usually have been around $1200 at the time.
There are strict rules about getting any and all repairs pre-authorized by the insurer. Everybody thinks their case should be an exception, but I can assure you it will not be. The only valid exception I know of is an emergency repair to prevent further damage to the vehicle while the insurer's claims office is unavailable to provide authorization and that better be an ironclad case, not a "might of".