I'm not sure if you should get a full roll cage, That would be alot of uneeded weight. Instead, you might want to consider just a roll bar, It would be much more practical.
You could make one that would just protect the part that you need protected, and thus would save weight from all that extra metal on your car that isn't really doing anything.

But if you still feel like you want to buy one, and spend all that money on weight,
https://securehost59.hrwebservices.n...=5&CID=TRAXXAS
It is a little pricey, but my cousin has one for his savage and that motherf***** is strong as hell. And accually it is really light for a full roll cage, my rustler has more weight in aluminum parts.