One of the least glamorous parts of our exterior remodel was adding spray foam insulation inside our walls. We were lucky to have existing insulation in our attic, but our walls cavities were completely bare. Considering last year we spent over $300 in January on our gas bill and the house never got above 65 degrees this was a completely necessary addition. We used a small mom and pop shop which was way cheaper but kinda lacking on professionalism. This seems to be how we get 90% of our work done.
The good news is the entire thing took about 3 hours so my freak out session was limited. The outlets easily slipped back into the wall and the soy based foam wiped up. As soon as they were done I could not wait to get the siding back on the house and start painting. I also couldn't wait to turn my heat on and see what a difference we had made. The addition of insulation cost us $2,400. This was pretty cheap (we had been quoted up to 5k), but, it was in part because they didn't have to drill through the siding or patch it back. Oregon gave us a tax credit of $340 so for the cost of a 3-day weekend in NYC we warmed our house, reduced our heating bills, and greened the earth a little. You can teach a 1920's house some new tricks.