It is made a lower quality model. My best guess here is less than 250 robux. 3D modeling programs tend to have a better edge than Studio in making smaller tools or objects with detail.
I have to agree with Operatik. You could either sell it as a one time sale of 500R$, or resale for 200-250R$ each.
I would also recommend trying to model off of real world references and blueprints to get a better understanding of the anatomy and functions of weapons.