All the public ramps in Caroline and Dorchester counties are free. Rolphs on the Chester is a pay as you go. I'm not aware of any others that are per launch. Kent and Queen Anne's Counties both require a permit.
There used to be a pay ramp in Bishops Head, Dorchester County, if I remember right. Near a packing house. Don't know if it's still there or not.
Been 10 years since I've been there