The MUPs in most cities are fee free. But the Wisconsin DNR is forced to charge fees for use of the the 700+ mile rail trail system. They need the money for trail maintenance. Fee is $4 for a day or $20 for a year. One pass works across the entire system.

I just pays me $20 each spring and forgets about it. I usually ride the trails about 40 times a year, so its only about 50 cents a ride. It was $15/yr until last year. It would be nice if the state government would cover the full cost, but as they have a $6B budget deficit, that is unlikely.

I've had a pass for 3 years and have never once been stopped by a trail monitor. I've heard of people who have been checked.

OTOH, I rode the Cannon Valley Trail out of Red Wing, MN one time and during a 40 mile ride, was stopped twice and asked to display my trail pass. Which I had purchased before starting my ride.