Cost will depend on how many cards you submit and how long you want it to take.
They will normally give you further discount (from what ive heard) if you have a lot to submit
Add the time of shipping to/from Australia, depending on what service you use to send it there
Ie Express shipping there will be 5-7 days and it usually take about the same amount of time to come back...
say 10-14 days in transit to and from + the service level (eg 10 working days) so roughly a month
Also, would anybody know if customs will tax your incoming cards (if the declared value is over $1k)
Been thinking of doing a submission myself, but just wasnt sure about the GST thing...
Clarence to answer your question you should not be charged customs tax if Beckett remember to mark the form as returned goods.
I did a large submission for the site a few years back that was of a high value and there was no customs tax because Beckett said they were returned goods.
If they don't just keep the records of what you send out and show this to customs and you should be alright. At least this is what customs told me at the time.
If you just want to try out with low-end cards, you can join a group submission club - look for jeffv96masters on the Beckett forum (grading section). I have done three lots with him using 20 days service at $5.50 each + $1 per auto. You send your cards to him.