The basic idea is that I give a discount when you make multiple item purchases.

For US and Canadian sales this means I take ~$5.00 off for each item in a multiple item purchase. For example my CD and Library are separately priced at $39.95 and $24.95, respectively. If you purch both, I knock the CD down to $35 and the Library down to $20. So your total price is $55 rather than $64.90.

For sales elsewhere in the world, the postage costs get in the way. For those I add back in the difference in postage between mailing to the US or Canada and elsewhere. For lighter weight items, this is usually about $5.00 but for heavier items it will be $10 or more.

So the following mess is what I've gotten myself into for this approach. A whole passle of buttons to accommodate all the combinations that make sense. The left-hand set is for US and Canada while the right-hand set is for the rest of the world.