frist, the diffrent clay , the good clay is Non-renewable resources， the really clay is very expensive. only exist in hanglong moutain, ding shan town, yixing.Some varieties of purple clay mining has become extinct. if your teapot price bellow $20 is of course not a really yixing teapot.

sencond, the diffrent work, Well apart from Clay,yixing teapot also pay attention to work, that is, the level of their skills. A good yixing teapot, it is necessary to correct the shape of symmetry.Mouth,spouts and Handles must be on the same line. a good work teapot using best clay' price is more than $40

third, the diffrent aritst. some good artist do the great work, they have the brand in china ineed the world and have alot of awords, the teapot have good collection value. for example , cheng jianming, wan xiaofang etc.

forth,The concept of subject matter. some good size was like by many people, for example, drop ball teapot, Antique teapot, Pumpkin teapot etc.

Simply stated, a finer pot makes a total difference.

First of all, better clay makes better tea. Unfortnately, many of the mines which contain good clay are now depleted or will be depleted soon. As a consequence, any pot which is made of good quality clay will cost you more than 20USD.

Better clays are more porous and tender. Although the way it was kilned also to some degree will affect this. As a result, the seasoning of a pot is greatly enhanced. Secondly, better clays do have mineral contents which are different that cheaper stuffs and therefore differenct qualities produce different chemical reactions, although I am not as astute on how this process actually works.

Better pots are generally fired at a much higher temp resulting in pots which are less likely to release raw clay odors in tea.

Note: Just because it cost more does not mean it is made of quality clay. There are many varibles which account for price e.g. artist, and artistry (although it is unlikely that a well known artist will use cheaper clays). I personally like less artisitc and more functionable designs. I would recommend buying something older atleast 20y old from a reputable vendor. The older the pot, the better "chance" that it will be made of more quality clay.

The only thing I can suggests is to try it yourself. Brew a pot in a cheaper pot and compare it to brewed tea that was made in a better quality pot. You SHOULD find that the tea is much smoother, better mouth feel and sensations and much more bright.

Its best to invest as much as you can from the get go. First, if you buy cheaper pots and later learn more about tea, chances are you will buy a finer pot later. Secondly, it is much easier to resale your higher quality pot even for a profit than your run of the mill crappy zisha pot if need be.