EPDM belt with fibreglass core. These are an equivalent to the normal belts used on Vorons, but they are rated to +135C. They are also black on the teeth side which, well, looks cooler.

For a 2.4 A/B belt, you probably want 4M. This will be about perfect for a 350, give you about 40cm of excess on a 300, and if you're building a 250, don't. (Alex this means you)

Price is per meter. Obviously it will come in one length, e.g. order qty 4 and you will get 1x 4M length, coiled as neatly as I can manage :D