Look for local suppliers in your phone book. I've got one here in Colorado that will cut the pieces to size and even polish the cuts cheaply. They can even make tubes for me if I request it...with a seam.
You might find it easier and cheaper to buy a cheap Jugsaw and cut it yourself. It does thoughn depend how much you want cut. -xoddoza
If you can do the cuts yourself and have the tools, I cut all mine with a table saw and a 60 or 80t plywood blade. It makes great cuts that can be polished and doesn't melt the material at all.
Sandpaper. Its much like sanding while painting. Start with a rougher (lower grade) paper and work up. Use a sanding block or a powered sander. If you already have the acrylic then do it yourself, if not, the bulk suppliers of acrylic in your area can usually match or beat the price of Lowes or Home Depot, with the added benefit of cutting it perfectly for you.
I just stopped by TAP Plastics (here) and ordered a lcd screen protector. They have lots of locations and reasonable prices. They cut, polish, and do custom orders. I saw a few people recommend them in other forums and I was lucky enough to live next to one of their locations. I'll report back with the results of their work.
The easiest way I have found especially if you are making more than one and want it exacltly the same is to cut your plywood template then use a router ( I think thats what its called) and just go around the ply wood with the plexiglass clamped on top, makes nice edges and is quick and clean.
