Unless your planning to build a very high end rod, the cost of rod building will save you some but probably not that much money. The true value in rod building lies in the fact that you can build it exactly to your specifications.
More of this is covered in the "Why Build?" thread in the archives.
Overall, building a rod really isn't that difficult, but it does take the time and patience to avoid hatsy mistakes. Even when problems occur, unless it is in a gluing or finishing portion, they are generally easy to correct.
Rod building is fun, and is a very enjoyable way to spend the offseason.