It's hit and miss really Steve. I have seen Blue NOS pairs hit £120 - £135 and NOS silver pairs for as low as £45. A NOS blue set sold for $175 a little while back on Ebay. I was after them myself but they exceeded what I was willing to pay.
A single chrome one would set you back around £40 - £50 at the moment. Blue ones are 'open' as they are the most desired.
I picked up a mint red one for £20 recently, which I thought was a good deal
