Sony uses proprietory active 3D technology for glasses. The sync is via IR. Sony 3D TVs are not compatible with 3rd party 3D glasses. Hence, you have to purchase 3D glasses from Sony only. The price of Rs. 3,400, though expensive, is in line with the prices other manufacturers of active 3D charge, namely Panasonic.
In 2011, a new standard for active 3D, namely Universal Active 3D RF was established. Many adopted this technology in 2012 - Panasonic and Samsung for example. But Sony did not, unfortunately. Samsung active 3D 2012 glasses are just $17.99 a pair (Rs. 1,300 in India). I, myself, purchased four pairs for my own use with Panasonic ST50 as they are perfectly inter-usable. There are many 3rd party 3D glass manufacturers who are selling Universal Active 3D RF glasses from $10 to $20 a pair. Panasonic continues to charge $75 (Rs. 4,000 or so in India) for their own glasses - not worth paying.
In 2013, Sony is going to switch to passive 3D after looking at the popularity, success and adoption of passive 3D amongst consumers, even though passive 3D is reportedly (?) inferior (I don't think so).
it cost around 25$ for the pair