Some domains are cheaper than others. One important element of the retail price is at what cost the individual registry – e.g. VeriSign for extensions like .com or .net – is willing to sell to us as a registrar.
When consumer demand for a domain is high and many hosting companies are willing to offer it through their portfolios, then that will drive retail prices down. Niche domains like .audio in turn might cost a lot more.
In the US, there is normally a battle for the cheapest .com domain prices. That is great for our customers. We strive to have very competitive offers for both, first year- and renewal prices.