You only get to step-up once per retail purchase. They take your purchase price and charge the difference from for their MSRP, which can be higher than retail. In cases where your card cost more, you only need to pay shipping. Generally step-up doesn't work too well unless you purchase near full retail price and step-up to a new product shortly after release, which will be selling for nearly full retail price. If you paid significantly less than retail than you'll probably have to pay a good bit for step-up. If the card is selling much less retail than MSRP, it may ultimately be cheaper for you to just buy it retail and sell your old card.