The easiest way to save money on a software project is to do a simple vertical slice of the application first. That way it can be proven possible, and by doing so, some flaws in the design and implementation will be found early. Better still, requirements can be changed for the remaining parts of the application without screams from the supplier or accounts payable department.
Trap: Don't start work on an initial vertical slice of the application until that small module has been completely specified. A full requirements-gathering process should have been done before the work commences at all. The vision of where the whole project is going should be clear.