adidas via eBay offers its adidas Women's Adilette Cloudfoam Plus Logo Slides in Core Black / Cloud White or Core Black / Gold Metallic for $18. In-cart it drops to $14.40. With free shipping, that's the best deal we could find by $4. They're available in select sizes from 6 to 11.
Frugal isn't smart if you put off replacing these things. Waiting too long can cost money or even endanger your health.