There is no charge to claim a listing.
Once it is yours it counts towards your plan’s listing allowance — Free 3, Pro 10, Pro Plus 30 — like any other listing.
What claiming does cost you
One slot against your plan’s listing allowance — Free 3, Pro 10, Pro Plus 30 — exactly as if you had created it yourself.
If you are already at your limit
You will need to upgrade, or remove a listing you no longer run, before the claim can be completed.
Claiming is free, but the verified and featured badges that owners often want alongside it are on the paid plans.