Is there a graph that shows the thrust required for a given airspeed?
For horizontal flight, thrust required is the same as drag.  Go to the specific graph referenced in this answer How close is the air resistance or drag force to be proportional to the speed squared?, and you'll have your answer, or close to it.

The specific graph referenced here is for "a conceptual two-seat light sport aircraft (LSA) designed to cruise between 80 and 100 kts".  A Cessna 150 or 172 might need somewhat more power for the same cruise speed.