In this paper, we describe a case study in developing an access cost model for WebSources in the context of a wrapper mediator architecture. We document our experiences in validating this model, and note successes and lessons learned. Using experimental data of query feedback from severalWebSources, we develop a Catalog and Access Cost model. We identify WebSource characteristics of the query feedback that are reflective of the particular WebSource behavior and identify groupings of WebSources based on these characteristics. We also characterize the Access Cost model as having High or Low Prediction Accuracy, with respect to its ability to predict access costs for the WebSources. We then correlate WebSource characteristics and groupings of WebSources with High or Low prediction accuracy of the model.