The same applies here as in Question 17. However, the options that are open will depend on how far the project has already advanced. Generally there are two options. The first is to seek and obtain more project funding. The second is to reduce the scope of the project.
Theoretically, a third option is to reduce the quality of some of the components of the project. However, this is not recommended as the impacts are usually marginal at best and at worst may lead to significantly greater costs during the subsequent life of the product.
More innovative and frequently very successful is to develop an alternative and more cost-effective solution to one or more of the project's objectives. There are techniques for doing this, such as value analysis, a technique which usually involves broad and expert consultations.