marble sample cupholder / coaster guard

I had some 4 inch marble samples* lying around. With the help of some poster putty, they make good coasters for my tv stands. However, drinks like to slide around on the stand and on marble, so a custom cover with a cutout solves my problems. The combo 2.75" and 3.35" are to support both a yeti rambler and a miir camp cup, and are taller to support the weight of the heavier yeti tipping over.Something like https://www.amazon.com/dp/B01M8NZQIN, but they're usually a lot cheaper from any brick and mortar store specializing in countertops.