Hi,
That depends on the deals you are getting! For example, if you're a getting a disc for less than $11 plus $12.5 for shipping = $23.5 = 1104 and if they are sending it through USPS, then you can escape from tax. Otherwise, add another 200 or 300 for the tax. I think even 20north will also work out in the same way. I would advise you to get a good deal on bunch of discs, and get it shipped through borderlinx or vpost.
Cheers!