I'd say the reason that those Sigs are $450 is because they are in 357sig. Its a good cartridge.....if you can afford to shoot it.
Check some area police supply stores. They will often get a wide assortment of firearms. Anywhere from seized weapons to police trade ins. There are some that wont sell to the public though.
I bought a police trade in Glock 17 Gen2 with night sights a few months ago. The exterior had holster wear, but the internals were in great condition. It shoots great, just like the rest of my Glocks. Not bad for $323.