You can build a rack yourself cheaper than you could ever buy a professionally made rack, but you will have to reduce the quality to do so.

You can build a rack that is about the same quality as a professionally made on for about the same amount as a professionally made rack.

But I think that $ for $ you get the most from a professionally made rack. (this is especially true if you aren't particularly handy)

Animal Plastics, Reptile Basics, And ARS all make exceptional racks. In many different sizes and styles.