IN Brewster , right at the mid-point of the Cape, Nickerson State Park is the best park with no HU ($18)-- very close to it is Sweetwater Park, with HU ($45)
Both nice campgrounds -- both very accessible and easy to get from there to anywhere on the Cape within a reasonable time.
Summer on Cape Cod is a traffic nightmare ... plan for it.
The Bike Trail runs from one end to the other, with a few breaks, and numerous spurs to other areas.
PM Me if you want more specific info -- we lived on the Cape for twenty years.