We had a local guy come round to quote for double glazing areas of the house, bit by bit (because we didn't think we could afford to get it all done, the house is half glass!).
Here's a pic of two of the current window panel units - each one consists of 4 panes, one of which is a window which opens outwards.
This same unit is used throughout the house - there 9 in total and other panes such as doors, 1st floor windows etc etc but I had the main panel costed....
I was very surprised at the cost which is just $1,320 which includes new frame for the window panel and new locks (total size of unit is 2550 x 2000mm).
Thought it might be a good guide for anyone who is considering putting double glazing into an existing property.
Moorf