Found this on mrs.january.com, and thought it was very clever!
Dissolve 1/4 cup of salt in one litre of hot water and add to an empty windshield washer fluid jug.
Add 500ml of Methyl Hydrate (about $10.00 for a 4 litre jug).
Fill to the top with water.
There you go – homemade window de-icer! Your $10 will get you about 8 jugs of fluid and you will save around $25 through the winter. Also, this will keep those plastic jugs out of the landfill