You can get a pair for 50$ these days, if you want absolutely the best, and live in USA Monster has sell on their Bitcauldorn RF glasses kit, its a full kit for 50$ on ebay.
it may be up to 60$ now, a month ago I got for 50$ (Initially cost 500USD if im not mistaken then down to 250$)
Anyway, these are real RF glasses so you dont have any interference issues and if someone passes by the TV the signal wont be blocked.
Not only you get an awesome (tweakble/ firmware updateble glasses) you get a converter from Infra Red tech to RF
Also they very light and rechargeable no batteries. And you can connect LOTS of glasses to same transmitter, but im not sure you can get just the glasses because anyway the full kit costs like a single pair of other brand Infra red glasses.
And you can still use IR glasses with these ones,
I just got my pair today and so far I like them, I also have a pair of xpand 103 and original Samsung battery glasses,
xpand are heavier but have larger lenses, I got my pair back when they were just released for full price and i like them
Also they are battery operated