Here is an excellent article about some of the more expensive weapons for which money is requested in the Bush Administration's FY2007 budget. The issue of cheaper weapons versus expensive ones rears its head at specific stages in the American procurement process. I liked the story of how the DDG 1000 started life as a proposal for a "low-cost destroyer", and then gradually had more and more tasks added to its capabilities. It begs so many questions. Was it a "trojan-horse" project, intentionally priced low and intended to be eventually a big ticket item? Or was it the brainchild of those naval officers who prefer a "mosquito fleet" (a term originating in the Jefferson Administration, as mentioned here), only to see their project taken over by "blue-water" navy enthusiasts?
Looking forward to possible threats is one of the jobs civilians demand of their military and naval advisors. It's a fraught business, and doesn't always lead to good public policy. I am reminded of the British planners who after 1918 decided that the most likely opponent for the Royal Air Force was going to be France! They didn't have to omit the fact that the probability of that was likely to be small.