Few things--
1. A running back/game is much more about the other 10 players than the back running the ball. Where was Derrick Henry before Tannehill? Where is Leveon Bell? Who were the Super Bowl rbs?
2. A running back's most productive contract is almost always their rookie deal. Some are productive throughout their second deal, only Frank Gore past that(kind of a joke).
3. The supply of running backs is large. CJ Anderson or any rookie class.
4. Running backs are productive very early in their careers.
Pay the passing game players--Qbs, Wrs, OTs. Draft 3 round and below rbs. Use the passing game to get a lead and end the game running. You don't want to be the Vikings with Adrian Peterson. Rbs that can catch and run WR routes are a different story. I'm not talking screen catchers but backs like Kamara and McCaffery that you can isolate on lbs and run option routes, etc. Pay them.