Have an own domain is a must if you are serious in business. It can increase people trust on your business. You will be more confident with your own domain.
At this time, there are so many domain registration provider that you can choose. Usually they come with good offer for you. Many of them offer domain with price under or less than $20/year. You are free to choose which one is the best for you. If you still have no reference, maybe you can compare them one by one.
You can starting by visit Pay Less Domain Registrations. They are an Australia’s domain registration provider for cheap Australian domain names like com.au, .net.au, .org.au, .asn.au, and .id.au. You also can register other TLDs like .com, .net, .org, .biz, .info, .us, .tv, and .eu. The price is start from $11.95 / year. With every domain registration, you can get free services and tools like Email Hosting, URL Forwarding, Domain Name Parking, and Renewal Reminders. What do you think?