Johnathan modellismo has a carbon fiber sheet 200x300 for 29.90euro. Same price but with 100e of order you don't pay shipping cost and it is more whith that 100mm!!! Attention I doesn't work for johnatan modellismo but I think I buy there my carbon fiber sheet for these reasons. I write this for italian's buyers
First thing first - safety: Make sure you've got eye protection and a quality dust mask (or better) as the dust from carbon fiber is not very healthy.
A cut-off wheel in a dremel cuts this sheet like butter. A carbide burr also works well for smoothing the surface off. A hacksaw works fine for straight cuts and a bandsaw with a fine blade suitable for cutting metal should work fine also.
I have tried using a scrollsaw with a blade designed for cutting wood and it went blunt very qui
I used a hand saw with metal blade and then a file to get it exactly to the size i needed. Could have used a dremel, but as it has been said the dust is not healthy, and with a power tool the stuff gets everywhere. And if you accidentially slip with your dremel you could ruin the entire plate very quickly.
WOW !! I am not used to construction with carbon materials but this sheet is simply an armor! It is absolutely stiff and I swet a lot in order to saw out a triangular piece from one corner (I sawwed 8cm!) It is much harder than aluminum.