The low odor rubber is pretty expensive at rubberstampmaterials.com, about $20 per sheet not including shipping. I found it cheaper here:
5x A4 sheets for $49, free shipping:
https://smile.amazon.com/Laserable-Rubber-Stamp-Engraving-Machines/dp/B01MAT50B6
$11.69 per sheet at a couple of places, not sure of shipping.
https://www.johnsonplastics.com/premium-low-odor-laser-rubber
https://www.signwarehouse.com/p/8-14-inch-x-11-34-inch-sheet-of-premium-laser-rubber