Why are some domains more expensive than others?

Some extensions (known as a "TLD"), eg .co.uk VS .com VS .co etc are more expensive than others due to the regulating body that controls them, the way that they work, and how they bill suppliers like ourselves. In the UK a non for profit organisation called Nominet is in ultimate control and as it's an organisation run by its members (which includes us), so the prices are kept low. Other domains extensions (TLDs) are more expensive as the regulatory bodies that control them aren't not for profit and they charge more. Some charge more simply due to supply and demand, and because they know they can get away with it!

Some of the newer generic TLDs released 2014/2015, eg those that end in words like ".property", ".world" etc, are even more expensive as they are considered to be premium domain names and the bodies that own the rights to them charge a premium.