The best place for used guns are the private sale ads on forums. I find a lot of my stuff using riverofguns.com which searches through all of the gun forums at once.
Save the money and use it on a TLR-1 instead. A laser will only slow you down. If it's dark enough for you to need night sights, it's also dark enough for you to need a light to identify your threat. However, if you use a weapon mounted light in conjunction with night sights, you won't see the...
I say don't do it. The P250's quality is nothing like that of the 22X series, or even the 2022. I also don't see a reason for a DAO. If you want another plastic pistol, there are better ones out there for a little more. You already have the Porsche 911 and Cayman, why get the Boxter?