After you purchase a domain name from someone there is just a small annual fee to keep it. It is around $10-$20 per year for .com and .com.au. It varies depending on your domain registrar (like GoDaddy, Uniregistry, etc) but there’s no reason why you should be paying significantly more than that.

Your domain name is a digital capital asset for your business. It’s extremely important to keep your credit card and contact details up to date at the registrar. Otherwise you risk the domain name expiring without you knowing.