Cost of visiting the "forts"

Does anyone know the cost (per person) of just going to either of the historic forts on your own and doing the tour and walking around? Not sure which one we really want to do, so cost for both would be great. There will be 6 of us, all adults.

According to the US National Park Service $5.00 pp will get you into both parks.

Or, anyone over 62 can get a senior pass for $10 that is good for life and will let you and 3 other people in any national park for free.