If you're not fussed about your coasters matching, go to your local tops tiles and look for a cheap box of square tiles, then put sticky felt pads on the back.
You can buy sheets of self-adhesive felt pads that you can stick on the underside - Stops them scratching up tables, and when you your toddler drops them, they crack but don't smash.
If you're not fussed about your coasters matching, go to your local tops tiles and look for a cheap box of square tiles, then put sticky felt pads on the back.
Charity shops for mats.