I have considered acrylic (plexi...) but I hear silicone doesn't adhere well to it so it's not an optimal material to use for baffles (or anything) within a glass tank. That said, I have not personally tried siliconing acrylic so don't know off hand. I have played around w/it though, including cutting. Not afraid of dust because in my experience it all melts from cutting or drilling so there isn't enough dust as far as I am concerned lol In fact it's hard to keep the two pieces sawed separate because right behind the blade the debris melts and glues them back together. Granted, I probably didn't use an optimal blade... but. Its not that cheap at 1/4" thickness... but you're right... probably beats the stupid $20/baffle quote I got.
I am actually thinking about going in a completely different direction w/the sump - no baffles, multiple tanks and buckets etc. There are plenty of 10 or 20G tanks around at reasonable prices. And bulkheads and PVC are also mostly reasonably priced. So I am at this point mostly just checking on the baffles in case my unconventional sump design turns out to be a dud.
Spacey