Used RV prices vary widely. Unlike autos, there is no stable, nationwide market that sets a benchmark price, plus there are sometimes large, legitimate differences by region, season, condition & options. Remember that an RV is a house more than a vehicle, so factors like location & condition have a lot more impact. Since there is no well-known market price and much less local competition, dealers are free to set prices however they like.
Much of this is our own (the buyers) fault. By focusing obsessively on discounts, we encourage dealers to price high and then offer a steep discount or sale price. A higher asking price also lets the dealer offer attractive-looking trade-ins, a plus in a business where high depreciation makes actual trade values shockingly low. Try to ignore the asking price game and get to the bottom line, what it will cost you to get out the door. Don't waste time trying to figure his asking price or add-ons.
Note that private sellers often also far off reasonable market values. They may not have researched prices and have an inflated idea what their RV ought to be worth, or they owe way too much money and are trying to get enough to pay off a loan.
Use the NADA RV Guide to get a rough ball park of the value. Check online sales sites for other asking prices, and check the actual selling prices shown at PPL's website. Those prices will be on the low side of average retail because they are actually private sales done via consignment, but it gives some factual data.
https://www.pplmotorhomes.com/sold-rvs