S.A rego gone up again!!

I can't beleive it. I've had my truck for less than a year now and not long after I bought it, I had to re register it. Now being a (commercial vehicle) HJ47 I undersand that it's a little more expensive than a private vehicle to register. I almost collapsed when I saw the renewal form for the first time, 775 dollars for a full year! Just to add insult to injury I just recieved another renewal as I only register in six month intervals mostly. Well whaddayaknow it's gone up again to eight hundred dollars for full year. Why should a vehicle that's being used solely as a recreational vehicle be subjected to such costs? There should be a way of proving that the vehicle is privately used to reduce these exhorbitant bills for the little battlers who just want a vehicle to camp/travel with. If there is a way I and many more I'm sure would like to know.

With regards, Jim.