Hmmm... I don't remember the name, but I assume you may have craft shops or what-not that have picture frames? Usually when you find picture frames you can also find numerous types of plastic sheets used in place of glass, some thick, some thin... Some a foot tall, some poster-sized. I would assume it's not that expensive, but I could be wrong.
Anyway, next week or so I'll be going back and I'll get the brand. It's a Maine craft store though, so it probably is of no use to you. I remember that a friend of mine used it to cover the side of a custom PC... He got a neon-ish transparent green, and it made a slight outward curve accross the computer. I'll be using the 1/8" clear sheets... 1/16" is too flimsy, and 3/16" is too thick to allow me to evenly heat it and manipulate it in time.
You can probably find some online though if you are looking into doing it this way, but it may be a bit more expensive depending on where you get it. Just search "1/8" clear plastic sheet" or similar in google. I at one point in time tried to find already smokey colored sheets and didn't find any dark enough, all requiring me to tint them anyway, so I'm buying the cheaper clear.
These aren't a bad price... 18" x 24" at 1/8" thick is $11.25... Buying two would give you 3' x 4'... Similar to what I am getting in store... But shipping is $8... Bringing the grand total to about $30 USD. :-/