No doubt that the war would be an awful one. But you guys assume that the West would have to occupy Iran, why?
The West stays in Iraq because it feels the investment in men and money is worth it. I admit that, if your numbers are right, 9 billion is high, but even if that's true you are talking about $108 billion a year from an $12.3 trillion dollar economy. That means that war only accounts for .87% of GDP (less then 1%). This at a time when the economy is growing at 3.4% and inflation is at 2.5% means that the economy can absorb the war in Iraq. That the US has lost 3,000 KIA is, frankly, peanuts. The US lost more in one day in World War 2 than it did in the years in Iraq.
So far the entire war in Iraq has not really cost much in the way of economic growth or even society. In fact, most Americans have hardly been impacted by the war at all. No one has stopped shopping, there is no rationing, there is no draft. Realistically, the war has been cheap.
A war with Iran would be more expensive, sure. But would it be affordable? Woudl it be worth the costs?
Would it be cheaper to create a no-man's land running from the Persian Gulf to about 100 miles inland of Iran than to occupy the country? (And yes, this has been done before with free fire zones in Iran).
How long would such a war last? Well, arguably until Iran made peace or the US and Brits gave up because the war was no longer affordable.
But lets say the Iranians didn't make peace or the West thought the war was affordable? Then until an alternative for oil was discovered and thus the reason for the war would no longer exist.
At which point the US and Brits could withdraw, leaving Iran and Iraq in a Hobbesian anarchy if necessary. Simply, it wouldn't be worth it for the US or the Brits to fight over a piece of dirt that has no value to anyone but those who want to own it. And why would the US and Brits want to own a lot of desert wasteland?
Morally that might sound repugnant. But lets face it. The West has fought colonial wars that meant thousands if not millions of deaths to indiginous peoples. The only reason why the West is interested in the Middle East is oil, and but for oil, the West could leave the Middle East much like it leaves Africa.
It's not like the West really did anything to stop the killing in Congo, Cambodia, Rwanda, Uganda, Sudan...... Why? Because those regions lacked sufficient value.