I neglected to mention that there is of course a charge for the Ditting burr trade-in program but IIRC it's about 13/ to 1/2 the cost of brand new burrs.
Jack makes a good point about new Mazzer burrs. These days, depending on the source, Super Jolly burrs seem to be mostly in the $35 to $50 range and Major burrs are in the $50 to $75 range. The conical burrs for the Robur and Kony are about 3X the price of major burrs but will grind about 3X the number of pounds of beans before needing replacement.
New York Central Coffee Roasters