Insignificant. I just paid $8.95 for durock at HD. If you can find it, I wouldn't think the 1/2" Densshield would cost more than 10-12 dollars. I would have preferred to use 1/2 inch Densshiled but could not find it anywhere locally. Everyhwere I called told me they stopped carrying it due to a drop in customar demand. Lowes only had 1/4" sheets.