Don't forget that you can do the same with insulated (double pane)units also. Some glass shops are set up to manufacture insulated replacement units. Every so often I save a friend or relative from dropping huge coin on replacement windows. They end up with a handful of fogged panes and decide to call a window replacement outfit. The slimy salesperson shows up, lies their ass off, and nearly convinces the victim that dropping $10-15K is the only solution. Instead, they contact a regional glass business I recommend, and they can either take the sashes in for repair, or have a tech. come out and do the work. All for a small fraction of the cost of a new window.