[Lindolirian]

I see what you mean. Isengard may have been a large and lavish Numenorean outpost, but it was still only that, an outpost. However, one has to remember that Saruman had many underground operations going on. He could have been mining in the Misty Mts. to the north or keeping barracks of Orcs under Nan Curunir. But still, all this was still probably not enough. My guess was that he was very deep in debt to Sauron who "loaned" him orcs and resources in an effort to build up his ally. Saruman seemed very unstable and his only option for survival was to spread over Rohan, not only for war in service to Sauron, but to be able to sustain himself.