Not to be too literalist, but it occurs that we buy military hardware from where we do because the object is not to actually acquire appropriate military hardware at a competitive price, but to further various economic goals.
For instance, it seems to this uninitiated civilian that the aircraft carriers are an absolutely absurd and asinine decision, a worst-of-both-worlds disaster, one so completely irredeemable that only corruption or criminal stupidity could explain it. Similar things can be said about the F-35 purchase, the Type 45 destroyers, Nimrod MRA4, and others.
I am a civilian with only a passing interest, but this much is clear to me. Final decisions on these things are made by politicians who have not been selected for this sort of decision-making, who probably don't see themselves as particularly invested in the results, have significant vested interests as regards short-term popularity among select groups, and probably don't have a passing interest in military affairs.
So, in short, don't we get a terrible, awful deal which risks lives and wastes hundreds of billions... because we're not really trying to avoid those outcomes?
Instead, we're trying (for instance) to get Gordon Brown reelected.