It's difficult to budget correctly for duty even if you have the right percentages because should customs decide to revalue the parcel the duty costs will change anyway. It can go down as well as up and you never know when your parcel will be inspected.
If you are ordering in findings, you may have to budget for them to be inspected for nickle content by the assay office as well.
Thank you I will just have to make sure I have the money then and not order as much as i need too. Which as been put on hold at the moment but researching all I can will help lols.