In regards to acrylic, the most important tools you need are fairly inexpensive. Most importantly, you'll need an acrylic cutter, that's needed to properly score it to make clean breaks (dremel works too but it's hard to get perfectly straight lines). Make sure you either leave the backing on or cover it in painter's tape before scoring/breaking, and you'll also need either some sandpaper or a file to file the edge down after you break it.
But the 3d model approach really is for the best. If you find yourself struggling to do it, you might be able to find someone to modify it to your specifications on fiverr for cheap.
I'd recommend a piece of red plexiglass. It's a little more expensive than cellophane, but it won't crinkle and it'll last pretty much forever. You can buy the stuff here. You can specify the size you need, or if you're up for it, just buy a larger piece and cut it yourself with a plexiglass knife.