Call Petair and they can easily give you a quote. I recommend you do this sooner rather than later as it can be the area that takes longest to organise.
You can't send them straight to Perth as they will need to go to quarantine first and that is in Melbourne.
If you didn't have a skills assessment prior to lodging the EOI then that would be grounds for refusal of the visa. I strongly recommend you speak to a registered migration agent.
Mandurah would be the better option as, while it is its own small city with a hospital and things it is also on the train line to Perth making working in Perth an option.
We lived in Mandurah for 8 years until 2016 and really enjoyed our time there. We were in the suburb of Dawesville which I would happily recommend. Feel free to ask me any questions