Like others have said, read, look at as many as you can to get a feel for what you want, then take your time and buy the right one. I bought my first class A motorhome last year, a 28 ft 2002 Safari Trek with an 8.1L vortec gasoline engine, it had been well updated by the previous owner or two with new tires, batteries, fridge, sine wave inverter, carpet, seating, safe-t plus, steering bell cranks, trac bar, flat TV, 400 watts of solar panels ..... all since 2014, and I paid just over $20,000 from a private seller (asking was $25,000, I countered at $19,000, we settled on $20,500) it was a thousand miles away though so recovery cost added another $1,200
As others have said, there will be things to fix / upgrade on any used older RV, even if the previous owners did a lot of work, there are still things that fell through the cracks, or just different priorities on upgrades. For me this has added another $4,00 or so to the costs doing most of the work myself. Some of it was small stuff, but small stuff adds up, here is a general list of what I have done to give you an idea, in no particular order:
$430 Fix brake problem, turned out to be damaged cap on the master cylinder, plus flushing brake system, most of this was RV shop rate labor, but hey when the brakes get squishy going down the road you stop at the nearest shop
$650 Dash air conditioner repair, it would blow cold at random, 2 full days in a shop I have been using for years, they 3 separate intermittent wiring issues, plus being a bit low on freon, they earned their money on this one.
$220 New LED sealed beam style headlights, I like seeing where I am going after the sun goes down and those old dim halogens just don't cut it. The new ones are still not as good as the HID's on my car, but they are close.
$650 new Koni FSD shocks, the old factory ones with 75,000 miles may have had some life left in them, but the new ones are a major improvement, no more porpoising going down the road
$260 front sway spreader bar, a suspension upgrade all wide track P32's should have
$165 Sumo Solo airless rubber springs, they helped, were easy to install, and I think great bang for the buck.
$125 new rear sway bar bushings, while installing the shocks I noticed the old rubber bushings were shot, front ones had been replaced by a previous owner
$185 See-Level 709 tank monitor system (open box amazon deal)+ $70 in custom wood trim work, like most motorhomes mine came with the nearly useless 1/3, 2/3, full monitor panel that always reads wrong on black and gray tanks, worth every penny
I think those are most of the bigger ticket items, however there were still numerous $20 - $150 items like, various marker lights, propane regulator (old one had a leak), propane extend-a-stay kit (old one was missing hose and valve leaked slowly), rear view camera (moisture in lens), headlight switch (old one had overheated at some point), CB radio (old one dead), electric heating element for combo propane/electric water heater (burned out), new Oxy-genics shower head (more better), 2 gallon water pressure accumulator tank (quieten water pump, and supply enough water to flush the toilet in the night without turning on noisy water pump)
Then of course there are pots, pans, BBQ grill, camp table, chairs, towels, sheets, pillows mattress pad, ...