Amazon doesn’t let you apply multiple credit cards to one purchase. This can be a problem when buying a high ticket item whose cost exceeds your available limit on one card. Probably not a good idea in general, but this happened to me recently when I wanted to use an American express gift card. However Amazon does let you buy Amazon gift certificates with as many cards as you like in any denomination you like from $5 to $5000.
The trick is simple. Figure out what the total cost is and then buy gift certificates on your different cards, e-mail them to yourself, and use them to purchase the item. This is a little easier to organize if you leave a little slack for the final card. Then you don’t have to get it right down to the penny. It’s also easier if you’re able to use supersaver shipping and live in a state where Amazon doesn’t collect sales tax, so you don’t have to figure that into your calculation.
I was in probably the most complicated scenario. I had a American Express gift card that can’t be used to buy Amazon gift certificates (some American Express rule I think) and since Amazon applies the full value of the gift certificate before charging the card, I had to get the number right down to the penny. Furthermore I live in New York for which Amazon collects taxes, and there was a shipping charge. So I went all the way to final checkout page to get my total, but did not place the order. I went back to the home page and bought my gift certificates. When they arrived I checked out again and applied the gift certificates. (I actually could have done this with one gift certificate but I got the numbers wrong the first time and had to do it over.)
Final result: gift card balance zero, and one new Canon EF12 II extension tube, Sandisk Extreme Firewire Card Reader, and Sandisk 32GB CompactFlash extreme card. Who knows? If enough folks click on the Amazon ads below. that combined with the $0.98 I saved, will actually have paid for the time I spent getting this precisely right. Who said humans were rational consumers? :-)