You get to pay for the brand name and something that looks cool...
First off, you need to verify compatibility, there are some glasses that don't work with all systems. I guess you could always return if they don't...
Also, in my avoidance of 3D, I still checked into it and people were saying that the most popular glasses for being able to work and work well with a multitude of systems, were frequently on sale with 1 pair of glasses AND an emitter for $50-$70. I believe that they were the MonsterMax one.
FAR from stylish like the Oakleys, and maybe something else is better for just as good of a price now since I haven't looked into this in about 9 months, but shoot... I can buy JVC glasses to go with my JVC projector (what you would THINK would be a perfect match) for $150 each, and they historically won't perform as well as the MonsterMax 3rd party ones.
2-M60s, VP180, 8-M3s, SVS 20-39PCi, DIY Sub, 8-Shakers, JVC RS45, Anthem MRX-1120