There only 2 hidden cost, i've found.
1. Is the shipping cost. It's usually 30-45usd. One of my suppliers only chargers me $6 but that is extremely rare.
2. The second is WU or T/T fees. Since it's the only way to pay to china, it's like $28AUD per transaction. About the same for both.
Make sure to add up all the cost to make sure you still make profit.