  The model of a side information "vending machine" accounts for scenarios in
which acquiring side information is costly and thus should be done efficiently.
In this paper, the three-node cascade source coding problem is studied under
the assumption that a side information vending machine is available either at
the intermediate or at the end node. In both cases, a single-letter
characterization of the available trade-offs among the rate, the distortions in
the reconstructions at the intermediate and at the end node, and the cost in
acquiring the side information are derived under given conditions.
