The cost of a domain name varies based on the domain extension (such as .com, .org, .net, .biz etc.), domain registrar, availability, and few other factors. Apart from new domain names, you can also buy premium domain names from someone else who has registered it before you, which is charge huge as their reservation time and value. Domain name investors often register premium domain names that are shorter, brandable, and easy to remember for the sole purpose of reselling.
For domain(which are not already register) cost will start from $9 and varies as their extension. In Nepal you can register from Rs.1000 to Rs.1500, depending on register company and domain extension. This is really small in front your business, right?