I recommend some comparison shopping. But, remember that US or Canadian resellers, although they may get a discount for volume, will also have to pay postage, and will need to make a profit. In short, you may or may not be better off ordering from a closer source. Remember too, that speed and good service may be more important than price in some respects. If you find a source you like, it probably pays to stick with them, even for the occasional more expensive item.
Mail can be surprisingly quick to and from Scotland, however.
I have had a delivery from Stornoway in less than a month from the time I dropped the mail in the box. It's perfectly all right to address mail in Gaelic to Scotland. The most important part of the address is the postal code anyway. Most of these sources take plastic. And your exchange rate will be better with a card than at a bank.