Look at getting a 50mm lens. Even the very cheap ones will produce amazing images paired with a FF camera body. You didn’t say what brand you are using but at least half my portfolio is shot with a Canon 50mm f1.8. Cheap looking, cheap to buy. Amazingly tack sharp images so long as you don’t shoot wide open and even then, it is not horrible. While not as good for portraits as the 135 suggested above, it should be well within your budget even as a college student.