Wow, you have spare time?
How about shipping some of it to me!
If you are willing to invest your own time for engineering and construction, and you have the tools, you can often make something yourself for less than it takes to buy it. However, you need to consider how much time you will spend doing it, and what your time is worth. Still, the fun of doing it yourself helps make up for that. Even if I can buy it cheaper, I will sometimes still make stuff myself, just becuase I enjoy doing it.
However, if you don't have the time, or you don't have the tools or knowledge to use them, it sure is nice to be able to buy something ready-made!
-- SS