My wife recently helped sponsor a worker and here is her thoughts on the process.
It's relatively easy. Immigration were very helpful and the process was pretty quick. The cost is pretty minimal. I'm pretty sure it was less than $1000. You pay for the first two stages and the person requiring the visa pays for the 3rd stage. A little bit of paper work required but nothing too complicated. Worth the effort for a good employee.
Here is a booklet which has all the information for sponsoring
http://www.immi.gov.au/allforms/booklets/books9.pdf
In summary (from page 4).....
Application stages
There are 3 processing stages in sponsoring an employee from overseas under the
subclass 457 visa program:
Sponsorship
The employer applies for approval as a standard business sponsor.
This is required to nominate an occupation for a subclass 457 visa.
More information on the Sponsorship stage can be found in Part 2 of
this booklet.
Nomination
The employer nominates an occupation for a prospective or existing
subclass 457 visa holder. More information on the Nomination stage
can be found in Part 3 of this booklet.
Visa application The person nominated to work in the nominated occupation applies
for the subclass 457 visa. This is the final step to obtaining a
subclass 457 visa. More information on the visa application stage can
be found in Part 4 of this booklet.
So the first thing that needs to be done is the sponsorship. This is an online form that can be found at
http://www.immi.gov.au/e_visa/employer-sponsored.htm
On page 24, it states that the minimum salary for (temporary skilled migration income threshold) for a sponsored employee is currently set at $49,330. This is to make sure the person can support themselves in Australia (for those people that don't have an australian sugar mamma/daddy). If the 'market salary' for the nominated occupation is lower than this, this visa cannot be used.