The multi-mode resource constrained project scheduling problem (MM RCPSP) is a generalization of the well-studied RCPSP. A literature review reveals applications of inexact heuristics or metaheuristics approaches for solving these problems, however, exact approaches are few and do not consider non-renewable resources, as well as, generalized cash inflows and outflows at every time period of an activity, as is the case in real World problem instances. We present two exact solution single-processor approaches: a breadth-first tree search procedure and a best-first monotone heuristic for solving these problem instances. The algorithms are thoroughly tested on problem instances using payment schedules generated for standard PSPLIB problem sets and results presented.