hi there,
when we were ready to apply we had no intention of using a migration agent as we thought why pay someone to do what we can do ourselves but after reading up about it etc we decided to use one, best decision we made.
the reason is they know exactly what is needed to get the visa granted and they do all the hard work all you have to do is provide the info they ask for.
As for the price, $3500 is a lot more than what we paid, we used ian harrop and they were very very good and the reason we chose them in the 1st place is because Ian used to work for australian immigration so again knew exactly what was required.
Hope this helps