The Desert Biome Pin was released globally by Sanshee for $10.99. It was released as merchandise for Terraria.
Official Product Description:
A Few Sand Blocks, Some More Sand Blocks, And A Little More Sand...
And you have the start of your very own desert! Don't forget some cactus and waterleaf plants or you'll be mighty parched.
The second pin in the the official Terraria Biome Collection! Stay tuned and collect them all!
-- Sanshee