About 300 yards north of the ferry pier on the seafront downtown you'll find Los Cinco Soles - this is a large tourist shop, but it has a fantastic selection of handicrafts including pottery from all over Mexico. The prices won't be as cheap as going to the potteries, but they are still very reasonable (and there are no potteries in Cozumel that I'm aware of!).
There is also a small store back from the seafront, I'm not sure exactly where but I think it must be on or around Calle 3 between Av 20 and 25. This is a more 'local' shop - it doesn't look much on the outside and I don't think it even has a name, but it has quite a large store behind. They sell a lot of handcrafted pottery and ceramics and the prices will probably be better - and negotiable. If I pass by that way I'll try to note the exact address and post it on here...
I found this information on another site ... don't know anything about it, but here is the info ...
The Talevera Store
There's no name on this open-air store. But the colorful merchandise spilling out onto the sidewalk in front makes it easy to spot.
Large selection of hand-painted Mexican pottery in a store just goes back and back. Some of the stuff is pretty kitchy but there's also a lot of really tasteful authentically hand-painted Talevera style pottery. And prices are a lot better than you'll see for similar quality items down on the waterfront. On Calle 1 between Avenida 20 and 25. Put your back to the flag pole on the waterfront and walk back into town. You'll see it on the left, middle of the 5th block back from the water.
I was dissapointed with Cozumel's shopping this time. The silver is cheaper in the states now. Haggled an 18 inch medium cut Figaro necklace from $119 to finally $47. Walmart has it for $39.50!
The shops won't even give you a second to look on the street before they start. They don't have a good selection either. Had to go to 3 Brother's and 2 Cousin's shops. Kept being told they had it. Finally found the piece I was looking for and overpaid after was less than half price.
One caution about buying pottery in Mexico. The bright beautiful colors they use to glaze their pottery contain lead. As long as you don't plan on using them for serving food or perparation. Otherwise they are prefectly fine for decoration.