A last minute flight PHL-CLE would be $300-$400. Assume $300.
If I can get that flight for 7,500 miles, than I have used each point for $0.04, or four cents.
300/7500=.04 [dollars/miles=miles value]
So if this is the route I am using my miles for, I would be crazy to sell them for less than 4 cents a point.