You can still be running a business without making  profit, let alone $20,000.

You really need to talk to an accountant before arbitrarily deciding you need an ABN.  It can be quite expensive to register as a Sole Trader or a Company if it is not necessary.

But to answer your question...it is not difficult to do the registrations yourself rather than pay someone else to do it.

Check out the ATO website and the government Business site...they give you all the information you need.