Over the past several years, I have found that clipper prices seem to range as follows:
$2,000 and under - bad condition; both house and engine/chassis have extensive issues; will often need towing to move; etc.
$2,001 to $4,000 - fair condition; either house or engine/chassis will have at least one extensive issue; several smaller issues in house and/or engine/chassis.
$4,001 and up - good condition; should be mechanically sound; May need some minor engine/chassis work; All appliances should be in working order.
A few items that I find should not factor into the price:
Cab A/C - these older AC systems are very expensive to repair ($2500+) and just aren't worth the expense for most owners to have done. So, most people find workarounds (using house AC with generator while on the road). Expecting the seller to cut the price of the RV because the cab AC doesn't work is just considered extreme.
Tire and batteries - these items are considered "standard replacement items". Every RV owner is going to have to replace these on a regular basis. Tires will need to be replaced every 5-7 years regardless of wear. Batteries can vary depending on type, maintenance and usage from between every 3-12 years. What type a person buys is completely dependent upon their personal needs and even if I bought and put in a brand new AGM 12v battery 2 months ago, the buyer may immediately replace that with 4 wet cell v golf cart batteries. Therefore tires and batteries should not affect the selling price of the RV.
Options - awnings, televisions, stereos, generators, etc. don't increase the value of the RV. Awnings are expensive to replace and it's reasonable to expect a 40 year old awning to be deteriorated, etc. Onboard generators of that era are fairly loud and for a couple thousand you can buy a couple hondas that are much quieter and more efficient - so again, there isn't any real benefit to them and therefore no good reason to pay more to get them. TVs and stereos are just to easy and cheap to put in yourself.
Definitions on above conditions:
Extensive issues - these are problems that will take a lot of manpower and/or expensive parts to correct. For engine/chassis, this is potentially ANY issue. If the engine runs a bit rough, it might just need a tune up, but it can just as likely need a new engine. Major rust or damage to the exterior - especially the fiberglass house. For the house, it will be things like: water damage to structure of house (e.g., dry rot in walls, floor or ceiling); warped or ruined paneling or wallpaper; fridge doesn't work; propane system leaks; etc. It also includes customization to the clipper that has rendered it into something less than what it was built as. For example: removing all kitchen appliances; removing sinks; removing shower stall; removing water tanks; removing majority of cupboards/seating/etc. While an individual owner may decide that removing these things is better, for the majority of RVers, these things are part of what makes an RV and will have to be added back in to make the rig usable - therefore if they have been removed completely, the value of the rig is severely diminished.
Smaller issues: for the engine/chassis, these are things like replacing rubber (hoses, belts, fuel lines, etc.), spark plugs, and so on. Basic maintenance stuff that might have been left undone for longer than reasonable but not a big or expensive chore to do. A couple running lights not working (if none are working, that could very much fall into Extensive issues). For the house, these are things like leaking faucets (easily replaced with standard faucets usually), re-upholstery work, replacement of stove/oven, replacement of cupboard latches, slightly worn woodwork, and so on.
Minor issues: for chassis, small dings in cab area, small dents in bumper, etc. For the house, trim that is loose or missing, decor/colors unappealing, etc.
Fridge - OK. Many people have replaced a 2-way or 3-way fridge (runs on propane and electric or propane, electric and 12v) with a "residential fridge". The residential fridge will only run on electric. If you will only use the clipper in RV parks and campgrounds with electrical hookups, then this will likely be OK for you. However, if you wish to camp in campgrounds with no electrical hookups (dry camp), you will have to: 1. have multiple batteries, and 2. have a generator and/or solar setup to recharge the batteries daily. For me, a residential fridge is a no deal because I always dry camp and I don't want to deal with multiple batteries, generator, etc.
Microwave - only going to work if you have electrical hookups, you have multiple batteries, you have a generator that you can run while you use the microwave, or you have a generator and/or solar system to recharge the battery(s) daily.
When buying it is really a good idea to have a mechanic look over the engine first -it can be hard to see at a glance if there is something wrong and often owners have done so much re-wiring over the years that you can't tell what goes where...
Also, if a seller won't let you operate any portion of the rig, walk away. I cannot stress that enough. Make sure you run water through the faucets. Light the hot water heater, light the stove and oven and make sure they stay lit. Connect to shore power and run water pump and fridge on electric and check all lights and outlets. Turn off everything and then turn on AC (on a 15amp household outlet, you should be able to run the AC with everything else off) and make sure it blows cold air. Disconnect from shore power and run water pump and check all lights. Run fridge on propane - make sure it lights and stays lit and make sure it stays cold (often the fridge will cool differently on propane and electric so don't be worried if the temp knobs are on different settings to get to the same temp inside - just make sure both electric and propane will cool the fridge to an appropriate temperature).
If the seller says "I don't have an outlet close enough to plug into", "I'm out of propane", "there's no water in the tank and my hose won't reach", "there isn't a battery right now", and so on, take that as an admission that there is something big that won't work and they are trying to hide it. To this day, I have not met anyone who bought a rig where the seller did not let them test any particular function and the buyer found that function worked when they got home. For me, when I bought my travel trailer, it was the water -the seller had put away the hose due to below freezing temps. Found out he had split the hot water tank and re-wrapped it with new insulation. Cost me $600 to replace the entire hot water system - the trailer only cost me $1800... WALK AWAY.