I live in a house built in 1880's I had a window that was rotted out on 3 sides and the bottom window that opens also was rotted out ...... I rebuilt my windows and put the window weights back in ..... if you was to look at my window now you would think it was never replaced ......
I feel that in my case it was best to rebuild them rather then replacement with a new window . If I was to buy a window like mine it would cost me alot .... but it cost me little over 150 dollars to build them .