I know this is getting a bit off topic......
If you want to read it, there is a link to the draft national rules on the forum for the Northern District Sporting Car Club.
One of the first rules of motor racing is "you will never win an argument with a scrutineer". This all gets a bit vague at times, I have been competing for around 7 years in my alloy caged car but I have never been asked for the logbook (I actually lost it and have ordered a replacement).
The wording on the cage rules were changed in the past couple of years to allow a bit more flexibility but I think this was to cater for drift cars that CAMS were trying to cater for. A lot of these things run cages done in Japan and some of them are a bit weird and wonderful. However, (and this IS JUST HERESAY) I have heard that some of the scrutineers down south have got so sick of how dodgy some of the cages are that they are recommending that these cars no longer be permitted in cams events.
But....its a simple fact that a cage is a major part of a car build and if you have not had it done right you are (a) asking for trouble eventually at an event and (b) your car won't be as saleable as most competitors do know about the requirments and will want to factor in doing a proper cage at some point in the price discussions.
The "nanny organisations" don't keep changing the rules, they were changed 10 years ago (!) and all cars that complied with the rules then have been allowed to continue race in under national level events. Even then we were given I think 2 years notice of the impending change so if you were thinking about building a car you could get it right."
It does not cost $4k to build a steel cage, my plumber is building a Group Nc Capri and he just had a steel cage done to spec for around $2k. My next Escort will be steel caged and I expect to spend around $2.5 to 3k doing that.
My over riding advice is read everything for yourself, speak to some cage builders, speak to the scrutineers in the categories and where you are likely to race and make your own decisions. Heaps of people get into a jam by accepting verbal or internet advice "my mate said etc". If you get it wrong you will (a) have to pay to fix it or (b) not be allowed to compete, and (c) most likely end up devaluing your car.
(You can read the cams manual in full on their website).
Cheers
Shaun B