Once you pay the ferry fee and arrive on island there are no further fees.
You'll stop at the Ranger station that is right as you exit ferry. This is where you'll obtain your beach permit sticker that goes on the driver side, upper part, of your windshield, and on the on the inside this year. This is no charge.
If fishing you will need a valid NC coastal fishing license or pass. They do patrol the beach and drove by us numerous times.
The only other expense would be the lighthouse tour fees. I do not remember what we paid, but its not much. They accept cards at the lighthouse gift shop and tour booth.
Make sure to bring clothes for any weather condition. It can go from hot and sunny to chilly and a monsoon in a short time being an island in the middle of ocean. Even if it doesn't storm, the wind can be pretty strong at times. The 2 hurricanes last year absolutely devastated the island. There are barely any dunes left to block wind across the ocean to sound.
We got sandblasted a few weeks ago there. Make sure to bring enough guy wires and something to bury your stakes in the ground or pieces of wood or brick. We weren't able to use our shower tent due to the wind.
Don't get me wrong, it's a majestic place. I just want to give you all the info I can to be prepared.
The ranger station also now has air and ice if needed. Davis shore ferry service will bring anything over for you on a ferry if needed also. I can't say enough great things about them. Very nice people that have a long road to rebuilding what they lost in the hurricane. Which is basically everything.