I'm also in the northeast (NH) and have a house with old (100yo+) windows. Are they good, solid, original wood windows?
I found a local window restorer who repairs and weatherizes old windows. With weatherization and a storm, original windows are as efficient as replacements. If you have original wood windows, the wood is possibly much higher quality than what you could purchase today if you went with wood replacement windows.
For my windows, most of which are 30" x 60", this guy's prices are lower than what it would cost to replace, and the restored older, original windows are beautiful and will last for far longer than any replacement windows. He repaired one window sash that had significant rotting and I took a class that he teaches so that I can fix the remaining windows myself.
Good luck!