In this paper, we study the operational availability of a complex technical system consisting of several components. The components are subject to breakdowns, and hence for each component a limited number of spare parts are held in stock. If a system's component fails and it can not be replaced immediately, due to a lack of spares, the system becomes unavailable until a new component is installed. Failed components are disposed of and hence, to keep the spare parts stock at an appropriate level, new components have to be purchased. We assume that only a limited annual budget is available for procurement, while any further procurement requires a considerable lead time. We investigate at an aggregate level what budgets are needed to attain a target availability level for the system. In addition, we develop various operational strategies for spending the annual budget during each year. Numerical results indicate that the so-called Balance Focussed strategy provides the best results in terms of system availability as a function of time.