Well in the US, I live in Florida and 42" 1080p HDTV at CompUSA (TigerDirect online) are going for $400-$500. Many TVs at that range go for around $500-$800 at Best Buy and CompUSA.
50" 1080p LCD HDTVs are around $800-$1000 now.
To get the extra 120Hz features or 600Hz Plasma thing it's an extra $300-$600 and I really don't find it worth it. The ultra-slim profile are usually $1500 or more. The 3D functionality is usually around $2500 (they have to have HDMI 1.4). The internet functionality (internet apps) built in are around $2500.
Either way I find the only worthy extra is the ultra-slim profile it's really sexy but otherwise I find the extra 120Hz or 600Hz boost not worth it. The 3D functionality is great but I don't really know if it's worth getting a new TV just for that.
Try Sam's club or Costco