I've heard a few perspectives. Some being that they were ridiculously high, and others being that they were at times lower than the taxes levied on Muslims. So which was it? Was it always the same, or did it fluctuate?
Edit: I'm particularly curious about the earlier caliphates.
I've covered this briefly in response to an earlier question here, drawing an example from the 17th-century Ottoman Empire. The answer is that it varied, not only from empire to empire but even from place to place within the same empire at the same point in time. There was no single standard for assessing the jizya, thus we see it applied in a whole variety of different ways.