In this paper we present a distributed query framework suitable for use in federations of digital libraries (DL). Inspired by e-commerce technology, we recognize CPU-processing and queries (and query answers) as commodities and model the task of query optimization and execution as a task of trading CPU-processing, queries and query-answers. We show that our framework satisfies the needs of modern DL federations by respecting the autonomy of DL nodes and natively supporting their business model. Our query processing conception is independent of the possible distributed architecture and can be easily implemented over a typical GRID architectural infrastructure or a Peer-To-Peer network.