I've done some storm windows and a picture window where I couldn't find anything new that fit for reasonable price. All were from eastern/northern white pine, The originals were white pine sapwood and they had lasted 100 years with poor maintenance, so I figured that new white pine would work just fine. As had been said, making windows isn't hard, but then it isn't exactly easy either. I seem to remember a lot of annoying math that was really easy to mess up.

Also, don't overlook how much work glazing is, especially since you probably need to use compound to match the look. If that can be subbed out, I would definitely recommend it. Glazing window after window of divided lights might just drive you bonkers.