Gun values will vary maybe +/- 30% from one part of the country to another. Seasonal variations too, as well as big-bore demand among Cowboy action shooters.
Here in the Southwest, .45-70 and .444 Marlin lever action rifles sell new for $400-$600. The .45-70 is more popular for the wide range of suitable bullets. I passed up a like-new Marlin .45-70 Cowboy and kicked myself because I bought a new one the month before for $700. The .444 is more limited by it's slow rifling twist rate.
In used condition as you described, $250-$300 is probably a fair price. The reloading dies, cases, and ammo add another $30-$40.
Good luck on the deal. If the bore is decent, it should be a good shooter.