Look up where you want to go, some are $10 a night, some more, some free. https://www.fs.usda.gov/activity/lolo/recreation/camping-cabins/?recid=10257&actid=29
It depends if you are using a tent or in a camper. If my memory serves me, the sign at one of the camping spots was $20/night for a camper. Hope this helps.
I did not see any formal camp sites so I cannot answer. I suspect that they would be reasonable.
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