Best, quickest, cheapest, safest way I can think of:
1. Turn car on with heater on high, all defrost (no floor).
2. Make sure you do step 1 so it can be heating up while you do everything else - every little bit helps.
3. Make some materials for some "salt paste" (rock salt is best, a ton of table salt will work too) - salt and hot water
4a. If you're using table salt, try to make a pretty dry paste. Use as little water as possible. Try to go for a play-doh consistancy (not quite possible but you get the idea of a dry paste from that).
4b. If you'r eusing rock salt and it is possible, grind up the rock salt into pretty smallish pieces (the smaller the better). Make a pretty dry paste, using as little water as possible. Try to go for a play-doh consistancy (not quite possible but you get the idea of a dry paste from that).
4b. If you're using rock salt but cannot grind it up, get enough very hot water that the salt starts to dissovle quite a bit but you don't want a ton of water in this. Shake it up, stir it up, get the water as salty as possible.
5. Let the water cool to be cool enough that you would use on a baby! Do NOT use this solution while it's really hot! But don't let it get too cold either or the amount of salt in the solution will be lower and give you worse results.
6. Stir/shake the solution on a regular basis, every time before you take some out of it (additional energy from friction will add a bit more of the settled salt back into the water-based solution).
7. Spread this paste all over the ice on your windshield. Rub it in, circular motions, significant pressure but don't get anywhere near close to enough pressure to break the glass (the only reason for the pressure is to give it a bit more friction for a bit more heat to help the salt and icey water mix better, NOT for actual physical force against the nice).
8. Keep stirring/sreading/rubbing.
9. Eventually you'll get to the point where you can finish up with a scraper.
I recommend just doing the driver's side of the windshield initially if you want to save time.
I can't think of a better/safer/cheaper/easier way to do this. Between the heater and the salt paste, you should get it before too long. Oh, and make sure you don't get frost-bitten hands/fingers with the rubbing!
-Jax