I know the answer lies someplace in the Manual or on the Forum, but I cannot find the information.
Is there a feature to show me the cost of opening a new hub before I commit?
You can use the base opening page to do this. Just do not press confirm at the end...
Just bear in mind that usually there's a huge difference in costs between medium and large base, and that opening a lower class base to upgrade it soon later is not a good idea because it's much more expensive!