Lots of weddings this time of year, and the giftcard holders often sell out.
So here is a free printable, digital file in high-quality PNG format. It is hosted at sendspace.com - perfectly safe and professional and easy to download. Just SAVE the file onto your desktop or into a folder. You can't "open" it online, usually. So save it, then print it as you need.
Cut the little "tab" on the back and use it to hold the front part of the giftcard in place. Attach the giftcard inside with a glue dot or piece of tape. The cut and fold lines are right there on the card - in coordinating ink. I think adding mica, glitters, or some stick-on jewels would dress the card up nicely.
I will post a JPEG version of it - click, let larger image load, then right-click to save, if you don't want the better-quality PNG one.