I'll second this, since everyone else seems to say you're wrong, but I'll say you can regularly buy a mid-tier rigid '90s mountain bike bike (Specialized Hardrock, Trek 820 through 950 MTB, etc.,) for an amount well below $150.
First, check the fork isn't bent. Ask us or a local fagbook bicycling group if you're not sure.
This way you at least have something to ride and start on.
Things to check: Are the wheels "loose"? When you lift the bike and spin the wheel, does the rim move side-to-side (closer to the brakes and then away?)
Chain should work just fine, paint should be in good shape. Make sure you can move the seatpost up and down and that the cables/frame isn't rusted to shit.
Test if each brake engages on the rim properly. If it's grabbing the tire or missing the rim, it might be something you can talk about lowering the price so you can get an adjustment made.
Make sure the steering column isn't "moving around" when you squeeze the front brake and push and pull (you don't have to push/pull hard, just back and forth a few times with medium force) on the bike while that front brake is engaged.
If it passes on this criteria, then almost everything else can be done by yourself quickly.
These bikes were built to handle off-roading and jumps without suspension, so they'll work great as just about anything else you want them to do.
They're made to be lightweight, made to be tough, and with the thicker tires they're rather comfortable. You can build them into hybrids or uprights, and I've even seen drop bar gravel bike conversions.
Most of the time if the gearing feels like the lever doesn't click and engage when you shift, then you can fix it with WD40 sprayed into the shifter assembly and working the shifter for like ten minutes or so. DO NOT replace the shifter units, as people typically sell you "V-Brake" or "Linear Pull" brake/shift units, which don't work right on '90s mountain bikes which use cantilevers and have a different pull ratio.