If I remember correctly, unless you have a season pass for Colorado State Parks, every time you enter the park you have to pay their fee, even if you are camped there.
I can tell you one park NOT to camp at, unless you like trains, highway noise & a lot of kids running around. The Jellystone in Larkspur, just South of Castle Rock. Not that it's a terrible park, its right off I-25, with train tracks between the interstate, & the campground. They pass the CG numerous times a day & all night long. Plus I-25 seemed to have heavy traffic all the time, I had to sleep with ear plugs in. As the train passes the campground, it's going uphill, and has 100 cars loaded with coal from Gillette, WY, headed South, and they go SLOW, one day we were waiting for the train to go by so we could leave the CG, and a butterfly flew in front of the truck. The train was going so slow, that the butterfly was flying faster than the train was moving! We spent the summer work camping there so pretty well know how things are.