I guess the question is "what do you want to achieve with your cage?" In my case it is not to race the car it is to stiffen the shell to eliminate any chassis flex and to add some safety by creating a solid mounting point to the harnesses and by the creation of a passenger cell. In this instance, and note I will only be using the car on track days not racing, the chances of lateral impact are reduced. In fact today i am relying on the original shell to ptovide all of my protection so anything I can do to improve this is a bonus.
NOTE: As long as it does improve the situation not make it worse.
To that end the question is what is the most cost effective method of achieving the gains required. Now if this is by finding a mate who can weld effectivly and then sharing the labour costs to develop a cage from materiels less that specified in the "Blue Book" but confident that the quantity to the material and the positioning gains the requireed strenght then that has to be the way to go. Now if that means that you use twice as much material then, in htis case as CDS is three times the price, then so be it. I would simply add triangulation where necessary to ensure that I was happy with the result.
