Oh puhleeze.... Iraq was well on it's way to becoming a terrorist haven before we invaded. We have set that back, which is a win for the US. Iraq containment m*a*y have been cheaper in the short term financially, but in the long term, it would have been more costly to us and the world because of damage to the economy and the compounding effects on the "maintenance" cost over time. A free trading, non-threatening Iraq will benefit the world and our economy. In your "zero-sum" type cost analysis, you are neglecting the increased economic activity that will offset the war cost.
Endless inspections only allow(ed) Iraq to continue to play the shell game with themselves in charge. It would have continued until they managed to slip a chemical, bio, or nuke agent out and would have been used against us by one of those terror organizations that WERE using Iraq as Afghanistan-II. WE are now in charge, and the shell game now has a limited life. We will find what they are hiding because we are actually looking for it as opposed to Blix and his blind eye approach.
Since the Terror camps were building and the WMD's (which you seem to think existed also) were being moved around or developed, it seems doing nothing but containment would have had significantly MORE risk and $ cost to the USA than containment in the long run.
I think you are underestimating the risks of intervention. Saddam's regime was stable and ruthless which kept lawless zones from developing. Saddams shiite slums may contain many would-be terrorists but they were contained and disarmed. Contrast that to fundamentalist slums in other Arab countries (e.g. Saudi Arabia) where the police don't dare to go except for a quick in-and-out raid. And when they do that they find all sorts of weapons and explosives.