You're comparing apples and oranges, if you're building a desk out of some 2x4s and a spare chunk of wood, and comparing that to $1000 products. Undoubtedly the manufactured products are lighter, more robust, and made from better materials. That isn't to say that these desks are more suitable.

One could build a desk from even better materials than the $1000 desk; maple, walnut, mahogany, stainless steel, brass, whatever. But it wont be <$1000 for materials then, let alone <$100.

I'm in favour of DIY and think it's admirable that you would build your son's desk yourself rather than buy, but I think it's important to be realistic about the costs and materials. These costs were a surprise to me at least, after getting into woodwork/metalwork.