The process is free as in gandi won’t charge you to migrate but newer registar might , and also if you DNS or other services the new service provider will likely charge for those.
[1] for .come .net .org and many other popular ones it is, however for some of newer Top level domains (TLD) they may have only one domain registrar and you cannot move. .dev is owned and operated by google alone.
Gandi afaik does not have exclusive access to any significant TLD so it shouldn’t be a problem