+1. A couple of companies made hybrids in the early 90s with quality steel and components. I have a pal who rides his Trek 750 on singletrack and loves it. Not a lot of room for rubber compared to modern frames, but you can probably put a 45c in the easy-to-find Trek 7** series, Specialized CrossRoads, Schwinn Crisscross, and Diamondback Overdrive. The caveat is that the lower end builds are cheap to find, but would require a significant amount of upgrading to be enjoyable. Others are harder to find, like the Bianchi Project 3/5/7, but would be easier to get on the singletrack right away.