First, do not skimp on a roll cage! Do you really want the "minimum" strength protecting you in a crash? Do you really want a cage built to a "budget"?
If you are in a driving situation where you need a cage, then you are in a situation where the driving is somewhat uncontrolled as compared to how HPDE's are conducted. This brings a completely new level of danger into the mix.
Take a look at these photos from a Boxster roll-over at Willow Springs. This was the result of minor contact between two cars coming out of Turn 2 at around 85mph. This car was the innocent driver - he was tapped in the rear, spun off track, caught in the dirt, and rolled 5+ times. It doesn't happen often but it can happen and a cage is there for exactly that worst case scenario.
Most cage builders at this time (2012) thought that the cages they were building were more than adequate - but the pictures tell a different story...
The cage in my car is one of the most stout and well built around. I know, that is quite a claim to make. Yes, its heavy and I have had to reduce weight in other places to account for the additional cage weight as compared to other Spec Boxster's with lighter cages.
People ask me: Is it heavier than it needs to be? Well, that depends on your definition of how strong a cage needs to be to keep you alive. There are no specifications that say build to this exact level and you are guaranteed to walk away unharmed. You build your cage and take your chances.
In my case, I wanted to maximize, not minimize, my cage to ensure that I had a higher probability that I would be able to walk away from totaling the car. I have a high paying job, a wife, and kids who fully expect me to come home from every race healthy.
So, what is your expectation? Is being disabled ok? Brain damaged ok?
I don't mean to be dramatic and get on my soapbox but this is the reality of the consequences of the decisions that you are making.
Take some time and think through what you want from your cage and communicate that to the cage designer and builder and then pay whatever it costs. Your life will literally depend on it.
I'll post the exact spec's of the tubing later today (don't have them memorized).
Here are some pic's of the cage in my Spec Boxster before paint:
