If you're talking about a domain name for a website...depends on what domain name you are after (i.e. if you are happy with just a .com or want a .com.au - which you will have to have an ABN for) prices also vary between suppliers, hosting is a pretty cut-throat business so generally you will pay much the same, but at the same time some suppliers are cheaper than others.

You'll also need a webhosting plan, to host the website from. To start off with you probably won't need a big plan, again shop around as there are some dodgy webhosts out there and others that will charge you big $$$ for not a lot...DF is in the business and it's surprising how many "kids" are out there trying to make a quick buck You also want to make sure you are going to receive adequate support from them!

Check out the ATO website for details on getting an ABN etc. I would be getting your business name registration & ABN sorted out first, then worry about hosting and domain names etc once that is all organised.

**I do apologise if I got the wrong end of the stick and there is another "domain" that I am not aware of that you were referring to....just blame my preg brain for that!