As a pro skater I doubt you would be able to claim anything. You would need to pay some tax in the first place and as far as I know you are unable to shift your tax liability from one business to another that you get little or no income from and hence pay little or no tax on. The general rule of prizemoney is that it has no general tax liability but any income earned from that money is taxable. Appearance fees are taxable as income.
On the flipside if you own a skateshop or are a PAYG taxpayer within a skateshop you could claim everything as a deduction
As long as the value of the good (excluding shipping) is below $1000 Aust (as indicated on the document the supplier needs to complete) then it will not be liable for duty or GST. Over that you may be liable for import duty and GST, and of course extra paperwork.