I live in an 80-year-old farmhouse, so I understand the reluctance to spend a lot of money on an old structure.

But FWIW there's a lot that can be done, inexpensively, to keep an old house warmer/cooler:
- use heavy curtains to keep air off the windows at night
- caulk every window and weatherstrip every door; makes a huge difference
- put reflective insulation on windows that aren't used all the time (the stuff with foil on both sides and bubble wrap in the middle); if you need some light through basement windows, use doubled-up bubble wrap
- put temporary clear plastic on the inside of windows you don't need to open (this is standard stock in every Canadian hardware store; you attach it with double-sided tape and use a hair dryer to even out any wrinkles; I assume it's widely available in the northern U.S.)
- heavily insulate the attic; this gives a lot of bang for very few bucks, and is much easier than upgrading walls.

All of this will save money, and make an old place a lot more comfortable.