The price of registration is deliberately small and the paperwork light, but it is not one-and-done. Under § 48.30 the fee to issue or renew a Certificate of Aircraft Registration is $5.00 per aircraft, and under § 48.100 that certificate expires three years after its date of issue unless it is renewed. So a Part 107 operator carries a standing, if trivial, obligation: five dollars per aircraft, renewed on a three-year clock. One eligibility detail rides alongside the fee — the person who registers must be at least 13 years old; an owner younger than that registers through someone who is at least 13.

Paying the fee is only half of it, because a registration that lives only in a database does nothing in the air. Section 48.200 bars operating a registered aircraft unless it displays a unique identifier — the registration number the Registry issues — and § 48.205 says how: the number must be legible, affixed so it stays on for the whole operation, and displayed on an external surface of the aircraft. The point is that anyone who recovers a downed drone, or an official who needs to identify one, can read its number without taking it apart.

In practice that rules out tucking the number inside a battery bay or behind a hatch. It has to be on the outside and readable, and it has to stay put through the flight — a label that peels off in the wind fails the rule as surely as no label at all. Registration and marking are a pair: the first puts your aircraft on record, the second makes that record mean something the moment the drone is in someone else’s hands.