If you see the same features (be careful, are they really the same?) you can expect two factors to be causing the difference in price:
1. You will pay some $ for the name of a branded card
2. All <b>hardware</b> is not created equal. You will normally find manufacturing shortcuts such as PCB manufacturing materials/coatings, Conector and mounting hardware differences, trace layout shortcuts, copper thickness, IC's that didn't make the Quality Control standards demanded of "premium suppliers" etc....
Finally, you may just find a smaller company with a great product trying to get some market share by offering at a reduced price. It's VERY difficult to get straight information (especially on a forum like this where so many people put their egos ahead of their science.....)
I suggest finding a small computer shop that has geeks in it who have some REAL experience and seek their advise... (in person)
Normally, with all features the same it is going to be subtle things like lifetime of the product and/or "tweakablility" of the product that suffer with no-name equipment. (But not alwayz)