This is a guide, nothing more. It does not account for vehicle condition, add on's, etc.
The prices for 2000+ models have pretty much followed this guide - until recently when the demand for all RVs has escalated. You can take the values shown here and multiply them by whatever you deem to be correct. Some buyers have admitted to paying 200% over the guide price. Now they wish they had not now that the buying frenzy is over.
Asking $25,000 for a rare 1980 "museum quality" Lazy Daze is one thing. Paying it would be insane. A knowledgeable buyer would pass on if it were priced at $3,000.
Some folks think the 2021 LD on the new Ford chassis invalidates the price guide. The new engine is a definite improvement. But, how can less than dozen delivered RVs affect the prices of all previous models? The same pricing formula is used for all models going back to the original Dodge chassis.
A word about add-ons. Sellers should NOT expect to recover what they spent on add-ons. How much can be recovered depends on the item. 80% of the cost of improvements to a home kitchen is commonly recovered when sold. The percentage recovered on other items drops dramatically. It's the same with vehicles. A working transmission is expected, so little of the cost of new transmission will be recovered. Hydraulic levelers are expensive, but some buyers could care less about them. An expansive solar system means nothing to someone who will never use it.
Buying: If you are not RV savvy, you should pay a professional to inspect the RV. The trick is finding a knowlegable tech. It takes several hours to check all systems. An honest seller would do things like have the refrigerator turned on before you arrive so you can see for yourself that it works. The seller would have enough gas and propane so that all systems could be exercised. No excuses.
It is best to buy from someone that has used and knows the RV and has service records.
The older RV's come up with problems you may not think of. The ones on the Chevy chassis have carburetors. Do you know a tech that can rebuild a carburetor? And they are way underpowered. Hoses and belts may be close to rotten. The list goes on. Figure on spending at least half of what you pay for one in maintenance.
Right now, 2021, there are several people actively seeking old LD's to fix up for sale. Fix up, means painting the interior to appeal to modern tastes. It does not mean that a nickel was spent on mechanical issues.
You will probably not find a "deal" on 25+ LD. But, you can overpay for one that has been sitting for years and be looking at a large investment in getting it in shape.