The keyboards themselves are usually pretty cheap. It's the new keys, switches, LEDs, screw and nut drivers, cables, powder coating, stickers, screws, springs, stabilizers, resistors, diodes, housings, cases, PCBs, controllers, paint, heatshrink, labels, solder, multimeters, snips, foam, clamps, drills, dremel, bits, epoxy, etc - that adds up.