Usually, a big part of overall project cost is the cost of resources. So reducing costs often means reducing resource costs. You can do this in a number of ways. For example, you can replace expensive resources with less expensive ones. Or, you can use as few resources as possible. Another way to reduce project costs is to look for tasks that are over budget. Try to reduce their resource and materials costs or even eliminate them if they’re not necessary.
Finally, feel free to experiment. Make whatever changes you need to hone your schedule. With Microsoft Project, you can see the effect of each change instantly, decide whether it’s beneficial, and then make any other changes you think necessary to produce an effective project schedule.