While I couldn't find anything for $0.18, here are some of my cheapest finds:
90-Degree Elbow of PVC Pipe Fitting (3/4" Slip) - $0.43 + Free Prime Shipping
Elmer's Glue (4oz Bottle) - $0.50 + Free Prime Shipping
Roller Chain Connecting Link (8 mm Pitch) - $0.54 + Free Prime Shipping
Makeup Blender Sponge - $0.79 + Free Shipping
Skull Mask Bandana - $0.86 + Free Shipping