The more expensive poles are lighter in weight. They have better quality adjustment mechanisms that lock more securely, and unlock more easily for adjustment. They are quieter in use, i.e. the interior tubes are shielded from banging into the exterior tubes during use. They're probably better balanced to swing more naturely. The finish is probably much better quality, and as is the aluminum in the tubes. Some of the expensive models have spring action shock absorption (which I don't like). The expensive ones probably are better contoured to reduce shock to the hands and arms even without shock absorbing spring action, i.e., they're engineered instead of being blindly and inaccurately cheaply copied. The more expensive ones also would tend to have more comfortable and higher quality handle grips to reduce shock.

On the other hand, the cheaper ones could be a great value, and the more costly ones overpriced for what you get.

Most outdoor shops rent trecking poles, so you can try before you buy.