No extra charge. We have done it before. Course almost 2 yrs ago, but doubt things have changed. You are paying to enter the park and have free reign, so guess it still not a problem. Going again in July. Really like the place and easy to get to.
Make sure to bring cash for the entrance fee, they don't accept plastic. $12 for adults, $6 for kids. Exact change is encouraged. Exact change is really encouraged for the taxis in Coz. The driver might try to tell you he can't make change, so bring lots of 1's and a few 5's.