For 2012 Samsung and Panasonic glasses are compatible and many are getting the Samsung cheaper glasses avail on Amazon or other places <$20
See it above under Customers also Bought
Amazon ran out of stock and 3rd party sellers are selling for elevated prices. This is a 2012 model so its likely no more are being made and 3rd parties are taking advantage of that fact and the positiive reviews leading to high demand. The 60" is the same price as the 55" because Amazon still has the 60" in stock (I think).
Correction: Panasonic informed me that ST50 series in 60 and 65 sizes will be out in 2 months (late May or June). Yes, it will cost more to get ST50 and they have made several improvements such as: Brightness, it will have a computer chip for smart TV, will allow smart phone or tablet to act touch screen remote, glass frame and other few other functional improvevements. I reordered my previous cancelled 65ST30 TV since I cant wait that long and price differential will be too great initailly between st30 and st50. The suggested MSRP for 60ST50 is 2100 and 2999 for 65ST50 and both can be pre-ordered.