As far as I remember, it is not a park that you can get the multi park pass. It was $15 for a car but I think there has been a price increase. This fee is only for the driving parts of the park. The visitors center and museum are free.
From what I can remember it is something like $15-35 per vehicle depending on the park. The fee is $20 for the little bighorn park. If you are visiting a bunch of parks the over the next year, you can buy an annual pass for $80. If you are over 62, you can buy a lifetime senior pass for $90 ($80+$10 service fee) or an annual pass for $20. Hope this helps!
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