The problem with the Barling to Alma interstate is that there’s a perfectly good interstate connection through Fort Smith. It basically makes the connection on a curve maybe 5-10 miles and 20 minutes longer. So the road isn’t particularly necessary in the first place. In the second place, a relatively high toll would cause folks to simply take the current route and add a few minutes to the trip.
The solution for a toll road is to do what they did in Austin - make the free road so bad that folks that can afford it don’t care about the costs to avoid the mess down I-35.