I would think by the time you bought all the materials, and PAID someone to weld and machine the parts, get the upholstery done, had the finished product powder coated etc it would cost 1 hell of alot more than these do.
Now in that same vein, if you were to have alot of spare time and consider your time to be worthless, didn't care how it was finished or how easily it is disassembled and packs up, I am sure a bench of sorts could be constructed for less $$.
Like all things in life, if you can make it yourself and have the time to do it that does not interfer with making money with that same time, there is a saving.
You don't actually believe there is $1.00 worth of material in a loaf of bread do you?
Time is money, so things that are engineered to work, are finished nicely and that require NO time or effort on the part of the user to obtain, costs money. It all boils down to what you value your time at.
KK