Renewal cost

 No matter from who or where you buy a domain name they all have to be renewed or a yearly basis. The price you pay today is a one time payment then when your domain name starts to expire you simply  renew it with you current registrar, this is who holds your domain name. As an example Godaddy.com renewal fee's would be around £10 plus per year dependant on what they currently charge. 

No one not even Apple, Microsoft etc own a domain name outright they all have to be renewed every year but you can do multiple years in one go. Currently most registrars will let you renew for up to 10 years at a time.