Please Make Private Room Purchase a One-Time Fee

[Noxifer]

Except everyone shares that same add-on through some magical Narnia portal.

Unless that door just leads to the corridor from which your room is accessed =D They just don't show that corridor because it's easier on system resources to timeskip past the potentially endless corridor :3
And to prevent people from saying it's not visible from the outside, that door might just as well lead to an underground access tunnel and.... well, excavating a new room and fitting in those automatic lights on the wall that pretend to be windows.... surely that would be a lot more expensive than just 300k gil :3