Tiles for Mosaics

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For my friend's birthday, I'm taking a breakfast tray and putting a mosaic on the bottom. I'm wondering where would be the best place to get the tiles and grout the cheapest.

I've looked at Home Depot. I've seen craft tiles, but they looked a bit expensive. I'm wondering if I should check out a tile/carpet place, but I don't want to buy a whole case of tiles, just a few in different colors. Do you have an advice?