It never hurts to keep your eyes open. I just hauled a twenty incher out of the local creek. When the water level went down a bit after raining buckets for a few days, it showed its handlebars.
The frame & paint were in good shape. The tires still had tread and held air. But the seat was all torn up. So: new seat, adjusted chain, pulled weeds out of everyplace, cleaned her up (girl's bike) and greased her up. And then I brought in my beautiful third daughter, Kassandra, who'd outgrown her old bike. She ADORED it. I adjusted it for her, and let her try it out. More adjusting and so forth. Now she rides it around and loves it dearly. And it cost me nothing. Nil. Zip. Zilch. Nada. Well, it cost me a new seat, a tube of grease, and an elbow of grease.