Probably can't. Saudi military strength in Yemen is not limited by budget, so doesn't help with a military solution. And the issues of control and religion and security over which the war is being fought can't really be made to go away with money, so wouldn't help too much with a political solution.

In any case, building up a city in Yemen would not strengthen the Saudi state and MBS's personal political power in the way that a new and rich Saudi city would.

Well he wants a city populated by hipster close to a trade route and also to use it as a way to normalize relationship with Israel and "experiment" a non-sharia area in KSA.

Such a project will require being careful about who gets there.