As Seilerbird said, they are all money pits, just some are bigger money pits than others. I feel the entry level price you are likely to find on a serviceable used motorhome is in the $20,000 ballpark, say $17,500 to purchase and $2,500 to fix the things that have fallen through the cracks. Even then you will still likely have numerous issues that will need attention eventually. Also expect to kiss a number of frogs before you find a prince at the sub $20,000 price point
Simply put a $20,000 gas motorohome is going to be something over 12 years old, there are lots of rubber parts that tend to age out around the 12 year mark, this includes, belts, radiator, fuel and brake hoses, suspension and steering bushings (including steering linkages, ball joints, motor mounts, bump stops...) If these have not yet been changed, expect them to start failing soon. Then of course there is other wear and tear, general upkeep, to contend with. I own a motorhome of this vintage which I bought 2 years ago, and know all too well here lately about unexpected issues, in July mine blew a hydraulic hard line 3 miles from home stranding me on the side of the road ($700 repair), then in August something started going clunk in the front end ($1,300 later it had new upper and lower ball joints on both sides), and last week on the way home 50 miles away the alternator went out, this is the project I have spent my afternoon working on today, I have the alternator and idler pulley out, and need to go to the auto parts store in the morning to pick up a new tensioner pulley before I start putting it all back together.