You know what, I'm terribly sorry, I actually misinformed you. I was actually talking about acryllic when I said plexiglass. That's what I bought, and it's the cheap stuff. Plexiglass is a bit more expensive than acryllic, and lexan is a bit more expensive than plexiglass.
The acryllic is just as clear as lexan or any other type of artificial glass. The thing is though, the .08" thickness piece of acryllic I have is 20x as strong as glass, whereas the piece of lexan I have is 250x as strong as glass. The lexan is also a lot heavier. The acryllic I have is fairly flimsy, and makes a "wobba wobba wobba" kind of noise when I shake it, and it bends. I think you might want to go with acryllic because of it's affordablilty, and flexibility. The .08" thickness is very easy to cut with a "glass cutter" utility knife, or just a regular sharp box cutter. I'm recommending it because you probably don't want your 3' diameter shield to weigh 10 pounds. I'm fairly certain that my piece of acryllic that's 18" by 24" weighs about 1 pound. So you figure a 3' diameter shield would be just about 7 square feet of area. Therefore, with a little math, we can know that there are 2.35 of my pieces to make the same area of a 3' diameter shield. Therefore 1 pound times 2.35 equals 2.35 pounds Lol. So if you were to use .08" thick acryllic, and were to make the shield around 3 feet in diameter, you shield would weigh roughly 2.35 pounds.
EDIT: Sorry I forgot to answer the first question! Lol. The acryllic is just as easy to melt as any other type of artificial glass. Might even take a lower temp to get it workable than plexiglass. I recall reading a thread where someone oven-formed their own security visor out of plexiglass by letting it melt over a clay form. I recall them saying the oven temp doesn't need to be over 150 F. I would assume that thin acryllic would be even easier to melt, so you would have to play around with the temp.
I am le broke. 
