I spotted a Trek Single Track 820 at a Goodwill store today. Shifted good. Chain and sprockets were in good shape. Tread was good, but the tires were flat. $49.95

I probably could flip it for a small profit, but I passed it up.

i have been hoping to find a Trek in the 900 series, a 930 even.

IMO, the 800 series Treks, especially the steel (older) models were great bikes, but probably not the best for making a profit.

Try to find 830 or 930 or above ie 850, 950, 970, etc if possible. Varies a bit by year, but better tubing & components are worth looking for, often sold at same prices (used) as lower models