cutebunnyThe majority of the cost is really in the case. You could source almost all of the other parts for about $60 less, but once you factor in materials and fabrication for a case, you'll end up spending much more. Unless you have easy/free access to like a CNC mill or laser cutter you'll end up spending more on just the case than the rest of the keyboard.
EppyKayactually, trying to buy the switches alone for example would run you a pretty penny, diodes, pcb and teensy are "cheap" but when you start adding switches and shipping costs for each of those components from the different manufacturers when you source them all on your own, it's more than 199 ;)