Any? A lot? Say a lens/body is $1000 refurbished, so with an one year official Canon warranty.
For you to give up the peace of mind and warranty what kind of price break do you need on a used version of the lens/body? 10%, 20%, 30% ? For sake of easy let's assume the lens/body is in perfect condition, in both cases.
Extra Credit: Due to depreciation difference, do you value used/refurb lenses different from bodies?