How important is maintaining the origional asthetics to you? Is the rest of the house filled with period details you want to continue to match? Do you have any sort of storm windows or is the one pane the only thing between you and the outside? In my part of the country many older houses have basically a second window pane on the outside that operates via a crank.

I have 6-ish year old vinyl windows throughout my house and they're wonderful. They open and close easy and there is no draft whatsoever. My Winter heating bills are about half my friend's house, which is a similar size and vintage. I swear it's about 10 degrees colder next to the windows in his place. You can definitely tell they're new windows, though. My house didn't have any real period details so it doesn't bother me. Ugly is subjective.

as long as the wood is in good health, restoration can be accomplished. There are specific tools made for cutting away the paint on sealed windows, making it easier to disassemble the window for renovation. I saw all this on an old episode of this old house. The weights were replaced with sealed springs, the single pane glass removed and the frames tweaked to make room for new double pane inserts. After reglazing and new weatherstripping, they were reassembled ...very trick. It retained the historic aesthetic whilst dramatically improving the energy efficiency.

For the rotting ones, perhaps new pieces could be made?

I hate those sales guys. Another way to go is to bypass them by finding a "handyman" who has a contractor license. When there are jobs just too big for me like the one you are speaking of, I can usually find someone through word of mouth who works on those kinds of projects. When you go to those window companies, you are paying not only the contractor, and the wholesaler, but a middle man to put you all togther, thus a higher price

Let me chime in here too then.... I've made a fair amount of money doing energy refits and winterizing for people, or saved friends a lot of money by helping them do it for free at drafty places they lived in. The last part of this is about sealing things up and is of benefit to renters as well.

Replacement: You can replace just the inner parts of the window yourself without excessive difficulty and get most of the same benefit of having the entire window and frame replaced. You still have to be careful to caulk and seal the hell out of things too though.

There is also the option of going to a hardware megastore like busy beaver/lowes, etc. and having them install windows, which can be cheaper than local contractors by quite a bit.

Repair: It is indeed time consuming, but it is pretty simple work and can be rather pleasant especially if you have a helper. There are quite a few basic home repair books that cover doing repairs on wood casement windows as they are often labeled in such books, and you will know a lot more about your windows and how to fix them should you have a sudden need to do so rather than having to wait and rely on some arrogant twit of a repair person that will often do a crappy job anyway.

So you generally get better work at a far cheaper price, and it is cheaper than going the replacement route.

All of the pieces that are cracked or rotting can be replaced pretty easily as long as you can cut something to the right size. Often these pieces wear down and need to be re-installed to take up the slack such as you mention.

In any case you should seal any windows you don't plan to open with caulk anyway, you can cut it with a putty knife later if you want to, and for windows you may want to open you can use a weaker expanding foam product such as the ones made by DOW that are silicon based. Do not get the urea or similar chemical base foams as they exude toxins, bond too much to surfaces and tend to over expand and cause damage.

Even newer windows (or doors) can often benefit hugely from the use of this easy to break foam, and it cleans up with water.

For a few dollars, usually around 3-4 depending on sale pricing, you can save a hundred bucks a year or more using this stuff. I even use it to fully seal up the secondary doors in my house since you can break it loose easily just by pulling on the doorknob if you have to get out quickly.

By the way, this sealing up also helps you keep your house or apartment cooler in summer.

Geoff,
Several years late, but for the benefit of the Topic, I just wanted to add that I've recently created a website at tinyurl.com/9dbzc9 which documents, with lots of good photos, our own work to restore our 1927 Sears type house windows, including the addition of internal thermal windows, all resulting in saving the great old windows and improving the efficiency beyond simply replacing the windows with vinyl things... which have already given some of our neighbors some significant troubles, in the past 5 years.

I hope this restoration info helps others in the future.
-Rod