Just did a quick (and therefore possibly inaccurate) search on Google.
UK military spending per year is approx £75 billion. For all the complaints that we don't spend enough on this, in Europe, it's only surpassed by Russia.
Elon Musk receives a salary of £77 billion per year from his companies.
Ergo, Musk (or elsewise) could fund a considerable standing army.
Could be another billionaire, I just went for the obvious one