I'm with steve although I've seen home cheapo advertise replacement for 200 bucks. But if your trim don't match up, look out. A used door is just buying someone's elses old door that would not slide any more and had moisture between the panes so what's the point of that. Sliding doors can run a few hundred to over a grand depending upon material and quality. Go for a vinyl or metal clad door. Good luck trying to find one that doesn't need a weightlifter to slide it. I'm beginning to prefer and recommend french doors which are about the same price.