SD Card - GoPro Hero HD
You shouldn't notice in major downgrades in quality from a slower card (which I'm assuming is the main difference between the "expensive" cards and "normal" cards you mention). Higher speeds are required for newer cameras (like the more recent GoPros) that shoot in a much higher resolution and/or frame rate that need to be able to write a lot of information very quickly to the card. You should be more than fine with a class 10 card for the original GoPro HD.