You must pay to enter the park and camping along the drive must be done in the campgrounds which are not expensive. To camp for free you must be backpacking
The park pass is a must to git in park unless you hike in wich is cheaper but doing what you want to do I'm not shor maybe in one of the cut offs but to do it for any length of time I don't think so
To go into the national park, I believe you need to purchase a park pass.
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