Hey welcome to the forums
Generally, registrars will not charge you for transfering a domain from your account to another person's account as long as you both are using the same registrar.
Now, for example, if the domain is registered at godaddy and the buyer wants it registered on namecheap, you would transfer it to the buyer's account using godaddy, and from their it is the buyers decision wether to change it's registrar or not.
To change a registrar of a doamin generally costs the same or a little less as the registration fee.
If your still confused, I can tel you specifically if you tell me what registrar you're using.
Brandon