I thought the same thing as the OP when I started building mine last spring. I thought, "Hey, the raw materials aren't that expensive, I can do this for considerably less than buying one..."
Ha..what you don't see in all that brew stand glory are all the little fittings, quick connects, valves, hoses, etc. That $hit adds up in a hurry. Would I buy instead of build next time? He!! no..building was half the fun and deciding what parts you want, how to make it work in your brewing process, etc.
The materials of the structure are barely half the cost. I wont claim a brewstand has better 'value' as the OP mentioned, but in my case, It helps with my brew day. I can make 10 gallons in the time I used to make 5, I can control temps better..and d@mn it..it was fun building. I would do it again.