Excellent question and one I’ve been asked a million times. Here’s the thing, with GM speedometers buying a used one is like rolling the dice and hoping for the best. After all, there’s a reason your gauge went out, most people don’t know this but the original stepper motors GM used were defective and eventually they all go out. That’s also why we replace all the motors of every instrument cluster we receive, not just the one that went out. If you replace your cluster with another used one there’s No Guarantee it won’t die on you just like yours did a few weeks after you put it in, probably right after the Junk Yard warranty runs out.
Even if you can find a used one for less than my cost I can assure you it won’t come with my Amazing Lifetime Guarantee and you’ll have a tough time finding one with the same mileage on the odometer as your vehicle has, do you really want to take it to the dealer to have the mileage re-calibrated?