When first launching a website, you have to register a domain and secure a good web hosting space for your website. The cost of domain name registration is about GHC 100 for a year and that of web hosting varies from web hosting company to company depending on the resources like bandwidth, disk space, etc that you may require. The higher the resource required the high the cost of the web hosting space.
If you think your job is done once you have designed your website, I encourage you to give it a second thought. Your website will not give you any benefit if it is not responsive. You will lose customers (both potential and existing).