People will always price things according to what the market has indicated they can get for it. From my experience I've seen dealers selling SR-22's from as low as $550 and all the way up to $670 for a new rifle. Add in tax and shipping and you're into it for $700+.
Most used SR-22's I've seen on the EE have at the very least a rail kit (which 9/10 people seem to add to their stock rifle anyways,) some BUIS, a foregrip, and at the very least an extra mag. These extras definitely aren't cheap, and again throw in tax and shipping and they become quite expensive. So take that into account and tell me again why they're overpriced, especially when the owner has treated the rifle with TLC from day one, and the market demand greatly outweighs the supply?