  We study the problem of a principal who wants to influence an agent's
observable action, subject to an ex-post budget. The agent has a private type
determining their cost function. This paper endogenizes the value of the
resource driving incentives, which holds no inherent value but is restricted by
finite availability. We characterize the optimal mechanism, showing the
emergence of a pooling region where the budget constraint binds for low-cost
types. We then introduce a linear value for the transferable resource; as the
principal's value increases, the mechanism demands more from agents with
binding budget constraint but less from others.
