Cotten ??? ... no idea what this is all about .... maybe someone else has heard of this.
Razer Saw - now this I know ... it's a small saw blade that kinda looks like a mitre saw that attaches to a large hobby knife handle. It's made by companies like Exacto or Excel and has a thin blade. It can also be used with a mini mitre box. They are a little bulky for cutting fine detail though.
Trusty #11 Blade - this is probably one of the easiest and cheepest ways to cut something out. Instead of cutting with the knife edge, use the other side and draw the back of the point along the seam you wish to cut. Repeat this procedure intil you have cut completely through the plastic.
Happy Modelling and God Bless
Robert