So, are you looking for just some kind of metal cabinet or a purpose built ammo locker? If all you want is a metal cabinet I would check out some used office furniture stores. Also, home centers would have new models, so you might check them out.
A major source of objection to a free economy is precisely that it ... gives people what they want instead of what a particular group thinks they ought to want. Underlying most arguments against the free market is a lack of belief in freedom itself.
- Milton Friedman