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 Z belt you probably want 5M. Technically 350mm needs 4.8m, 300mm 4.4m, and if you're building a 250, don't. (Alex this means you) However, should you do it, 250mm is 4M exactly.

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