Yes they do work, but they are a bit of a hassle to use and don't really extend the range of the GSN that much. I've heard the wide gets around 35mm and the tele gets to about 70mm. You also have to focus with the camera then transfer the settings to the lens.
If I need a focal lenth too far from 40-50mm I just use my SLR (but don't tell anyone else in the forum, they will all point at me and laugh).
As for the price? I bought some on ebay as part of whole set with a camera, I can't remember the price. I ended up giving them away to somebody from this forum.
The close up adapter is kinda cool if you like doing macro shots.