How Do I Get A Coin Out That Has Been Graded...

I use end plier cutters. They work great.

One word: Dremel.

As noted the best way is to use a Dremel type tool with a cutting blade. Or any saw with a metal cutting blade. A saber saw works but the main thing is to make sure the slab is held securely in place. A vise would be a good suggestion. Cut off as many ends as possible and the slab will just open. Many say to use pliers or side cutters but if you are not really good at that, splinters of plastic will fly all over and you don't get seconds on your eyes. Regardless of what you use, always wear safety glasses just in case. If you do not have a power type tool, a hack saw or copping saw will work too but takes time. When using a power tool while cutting the ends off, you'll notice if you do not move fast, the plastic will melt back together so you have to move rather fast.
Or you could just use a Butane torch and melt all the plastic off.