Last year we took route 30 across Ohio to avoid the toll roads, then picked up route 24 after going around Fort Wayne on route 124. As already mentioned, route 24 (and route 30) is a good divided highway. IIRC, the speed limit was 55mph. As a heads up, after Logansport, route 24 becomes a 2 lane road. We had originally planned to stay on 24 all the way to MO, but got tired of the slowdowns and traffic lights and picked up I55 in IL.
If you are heading further west, route 36 all the way across MO is another good divided highway.