No it costs the same, the reason they do it is that it’s slightly more difficult to spoof a real number sender ID because most gateways will verify ownership by

No it costs the same, the reason they do it is that it’s slightly more difficult to spoof a real number sender ID because most gateways will verify ownership by sending you a text on that number before letting you send outbound from it, where as they have no way of doing the same for an alphanumeric sender ID