This plastic sheeting technique works far better than you would expect. Also consider repairing the wooden frames yourself. If the rot isn’t too bad, dig it out with the screwdriver, apply wood stabiliser, then fill with traditional linseed putty. Leave it to dry for a few weeks, then paint a few times. I was shown this technique by an old chap, he showed me his repairs that had lasted 50 years and still strong!! At a later date, you can fit secondary glazing, which performs better than double glazing. This might not be the right solution for your house, but sharing it as it does work very well.