Sounds like you lot said it all Cage spec is purely down to what the motor is being used for,as Lara said weight up high does not help with body roll or side slope angle.For most "club" situations 1 3/4" CDS is well up to the job of saving your neck,there is two ways to go either very stiff i,e thick wall tube or the more norm 2.5mm wall CDS.
In the event of a "BIG" roll i would rather the cage deform and absorb the energy of the impact than it be still straight as a die.The nergy has to go somewhere and if the cage dnt take it your seat mounts and then your back/neck are next in the firing line.
As for buying cheap it,s up to you to me it,s like buying cheap crash helmets you do get what you pay for.
Chris