An agency is a must, it would be very unlikely you could do it on your own, actually I doubt you could. I went with one and they charged me and my fiancee £1200 on top the £1000 visa.
The move will cost you allot of money,don't expect to do it cheap because you won't, also its a long process and took from thinking of moving and to me being in Aus it took 2 years. Also don't forget that you will need money to get your selfs on your feet when you get to Aus.
Your costs would be
Visa
Visa agency
TRA (Trades Recognition Australia)
medical
flights
shipping (if you need to ship anything over)
Hope I have help
I know allot of people say you don't need to go through an agency, I made the mistake of getin my TRA (trades recognition Australia) that you need to get befor you can apply for a visa and applied for it off my own back and it was rejected I hadnt givin know were near enough info that they wanted, and my trade is in the wanted list of trades, so I went through an agentcy and they went through everting I needed to do and they would check everything first befor sending it off, and guess what I was accepted! and then they did my visa with me.
This is how much info they wanted off me just to get my TRA
1. where I did my apprentiship
2.exact dates of when I started and when I left
3.who trained me
4 how i improved day to day in my training
5.what tools and equipment i used in all my jobs
6.what were my day to day tasks in all my jobs
7. go through all procedures of all jobs that I would ccome across
8. show pics of me working
9. get VERY detailed refrences with the aboe info in them
10. get all my qualifications
11. copy of passport
12 two pass port pics
Once I got that then it was a simaler amount of effort to get visa, so its better going through an agency rather than wasting my time getting somthing little wrong getting refused and then having to wait two years befor I can re-apply.
Also if I didnt get visa the company would refund my money.
I have done the move this year so I know what is needed to get a visa in 2008.