i find that i don't really need a knobby tire for dirt/gravel/off road, as long as the tire is high enough volume. i'm currently using these $30 eastern tires on my 26er everywhere drop bar mountain bike thing and they kill it on asphalt, single track, gravel, dirt, everything i've tried so far. even on loose, steep climbs they have plenty of traction.
https://smile.amazon.com/gp/product/...?ie=UTF8&psc=1