Unfortunately Afrihost don't currently offer a domain registration reseller solution.
The easiest way to get domains registered would be the order form available on the Afrihost website: https://www.afrihost.com/site/product/domain_registration?src=website_nav
If you opt for a hosting package, you can drop the registration costs but this is only more affordable if you intend to do hosting: https://www.afrihost.com/site/product/linux_hosting?src=website_nav
If you want to drop the registration costs without taking up hosting packages, you can opt for a Reseller Hosting solution.
The caveat however is that you'd have to do the registratoins manually.