For you cost conscious types,
I have used a couple of products to help insulate my apartment, which is very drafty. In particular the clear shrink wrap that goes over the windows. I have found the 3M brand version of this product works quite well, becoming very clear after shrinking with a hair dryer. I have also used a brand called Frost King which does the job, but wrinkles formed in the film during extrusion at the factory do not come out after shrinking. If you are a nut like myself, anything that diminishes the view from your window is a severe no no. For my money 3M is the way to go, but both products GREATLY reduce the draft through poorly insulated windows.
I hope mentioning brand names is not taboo, but if it is, then I guess I will hear from the moderator.
Good luck making your home more comfortable.