The retail cost of the individual tenons and cutters is $309.88 based on Hartville Hardware prices. I'm not including the 5mm cutter that comes standard with the DF500...why do I need to pay for one I already have?

They sell the components bundled in a systainer for $345. What it amounts to is they're charging you $35.12 for the plastic Systainer box. If you don't care about the bulky box then you're better off ordering the contents individually from Hartville with free shipping.