Not the absolute cheapest I've seen it on OzB, but cheapest I have seen it for a while.
Logitech G815 LightSync (920-009222) RGB Tactile Keyboard
LIGHTSYNC Intelligent RGB Lighting
Low Profile Mechanical Gaming Switches
Ultra-Thin Design (22mm Total Height)
Aluminium Alloy Top Case
Dedicated Media Control with Edgeless Volume Wheel.
$175 delivered