Do you mean in one party or total number of people in the park? Sorry, your question is not clear.
I live in Vandenberg Village and I got the card for free. From what I know they dont charge yet but it might have changed since I got the card a while ago. Be aware that they are not open after rain. The trails are awesome specially if you mountain bike.
If you have a recreation & parks card you can bring one guest. Residents of Santa Maria and Orcutt can get cards at the information center in Los Flores for free. Non residents pay a small fee. As far as I know those are the only limits.
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