I don't know/care about who is the cheapest. It's not just about price for me, it's about flexibility. I have to be able to control the domain name. I also don't want to have to leave my couch, print papers, fill them, tell people about my deepest secrets and call someone everytime I have to add a new subdomain.
If you are like me I recommend name.co.zw . I don't work for them but I also use their services. It will take you less than 24 hours to register your domain
Most ISPs will also register a domain name on your behalf.