Several registrars will sell to you at wholesale rates, and you resell at whatever price you can get. For example, you could buy registrations for US dollars and resell for Bitcoin. This means you have to handle payments though. I believe that GoDaddy has an agency programme for "resellers", this means that they handle the payments for you. If I start to promote the sale of my names, or start buying names, then I might sign up with a registrar like GD to simplify transfers.