This is the practical thing to get right before you arrive, because sorting it out at the gate wastes twenty minutes.
The National Seashore lot takes the federal vehicle fee — the same $25 day pass that works at Coast Guard, Nauset Light, Marconi, Race Point and Herring Cove, and the same $60 annual park pass. Cards only; the park handles no cash.
The Truro town lot immediately adjacent runs on the town's own system: a season sticker sold to residents and taxpayers, and a daily rate for everyone else, both set by the town each year. A National Seashore pass is worth nothing there, and a Truro sticker is worth nothing at the park booth.
Which you want depends on how you are travelling. If you are on the Outer Cape for a week and beach-hopping, the park pass or the annual pass wins easily because it covers six beaches. If you are renting in Truro for a fortnight and using this beach every day, ask your rental agent about the town sticker before you buy anything.
Both lots fill in high summer, though later than the Eastham beaches. This is usually the last of the six to close on a hot Saturday, which is precisely why it is worth the extra twenty minutes of driving.