Our house is rundown & uninsulated, and the property owner refuses to do anything about it even though actual *breezes* coming out from under the kitchen sink is obviously NOT "reasonably weatherproof"
One of the first things we did was hang blankets. Find the most reasonably attractive twin blankets you can at the thrift, or rummage sales or whatever. Then you can either nail them directly in place, or sew loops along one edge and hang them on a curtain rod. Put one over every door & doorway in the house. If you can, put *two* over each external door. You'll be shocked at how much this cuts down on drafts & chills.
Also hardware stores sell "draft stoppers" that screw onto the bottoms of doors; they have a rubber flap that "sweeps" the floor & seals any gap down there. People used to use long narrow sandbags laid up against the bottoms of doors. that gets inconvenient fast, though, as every time you go through a door it gets displaced.
This winter I might hang blankets over the windows too, or heavy fabric, if I can find decent looking stuff for cheap. I'm thinking I'd fasten them at each upper corner with a loop over a hook and during the day unhook one corner so it just swings down & hangs along one side of the window. Wait, DD will be pulling up by then. Hmmmmm ...
I second the suggestion about salvage yards. If you can't do that, then layers of cardboard & duct tape might work? Ugly tho.
We cruise our port district in autumn for free broken pallets and chunks of wood. They're fuel for our fireplace, which cuts down on the amount of electricity we use. We never get anywhere near enough for *all* winter, of course, but enough for quite a few cozy evenings with the heaters turned off.
Oh, and buy everyone several pairs of thick, sturdy socks and a cozy bathrobe! And plan on cooking a lot of meals in the oven!