If you have small feet, or can squeeze into kids sizes (I've heard from girls who wear 7 that fit into kids 5) you can find them at Marshall's or TJ Maxx or similar stores.
Knockoffs too. I have bearpaws. They're not $20, but they are $120 either. I think I paid $65 including shipping for mine. Same thing, real sheepskin, just no stupid tag sewn on the heel that says ugg. Love mine, asking for a second pair in a different color for Xmas.