I think that usage of 3D model (with royalty free licence) in this way should be OK (you cannot only resell the 3D model).
It can be only problem if the car model is branded (BMW etc.). So if you want to make real posters for selling you would maybe need assurance from the brand owner.
But 250 copies is not so big amount so probably you don't have to solve it.
Maybe somebody else give you more info. )))