I think it's $25/night. But you have to register over the email. Look at the website for details. It's a great option compared to sites around it.
Sleep in car if you want but why pay. Just sleep in car almost anywhere near there...
I think I paid around 25-35 USD per night for a "RV" camping spot with a van. You would probably have to do the same if you wanted to park your car and sleep there. I don't think you officially need a tent but you may be able to spend a little less with a "tent" camping spot.
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