Depends on condition.... i personally wouldnt pay over 100 for it...but then again, i'm not into milsim markers at all. To someone like you who is looking to purchase one and has interest in this type of gun, i'd try and keep it below 225.
I dont know man... look it up yourself, the gun is 349 new on sale (regularly 430$)... So like i said, depending on condition, my guess is that it could fetch 225.
A gun is worth what someone will pay for it.... So now that you know the price for one new, find out the condition its in, and then base what you'd pay for it according to how much YOU think its worth.