Obviously it depends on the total value of sales. When you are dealing with a large value then you will want to save as much as you can from the taxman. If it is a small amount then don't bother!
Actually it is free to register a business as a sole trader in Australia, just visit: ABR.gov.au
Your trading name is your personal name, unless you wish to register a Business Name, which last time i check was roughly $150 and you register through Fair Trading. Though a business name only gives you rights to it within your state, whilst a company name gives you rights nationally.
If you are planning to make at least several hundred thousand during your first year, you can register a company (ACN) as well as your ABN for tax purposes. Which you can do online through law firms for roughly $500.
here's only P300 if you want to deliver the registration papers to your house via air21 add P75 so about a total of U.S.$9.38 in your currency. if i were you do it so you can also advertise locally.
It depends. If your making thousands of month you should register your business, but if your earning some bucks you don't need to register your business.