Send (or borrow from the library) Terry Meany's book, Working Windows.
Also go to John Leeke's site (historichomeworks.com) for much excellent advice. John's books on window repairs are great!
Learn to do this yourself. It's a completely do-able, small scale (meaning only one window at a time) project. It takes a huge amount of time (that's what's costly about it), but the investment needed in tools is not bad. The materials costs are usually very modest, especially if you don't have to replace rotted pieces. The skills are fairly easy to learn, and you will get better and much, much, quicker by the time you've finishd your house. The amount of strength needed is limited, though it is not neglible. What's really necessary for an outstanding job is patience and being willing to be detailed about it. And because it is somewhat seasonal, the project stops when it gets too cold, so you have a built-in excuse to take a break.
Rehabbed older wooden windows can be made as energy efficient as modern windows. And when they need rehabbing again in another 75-80 years they can be done, again. You'd be on your second set of of "replacement" windows by then.
I have 30 double-hung sash windows in my 19th c house (and another 75+/- in my barns.) I'm working my way through them.
L.
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THey are in Evanston IL
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