A new mousepad. I don't know how much it cost, but it was on the low end and I got it from a local book shop to replace an aging, unusable one last March.
In the Teen Titans Go! episode "Uncle Jokes", Robin says "Ground cow" in Asian airings instead of "Ground beef" during the cow with no legs joke, thus making it unfunny.
My desk is wooden with a thick felt covering. The mousepad is just to give the mouse a steady surface for it to travel on.