Just like any other article of clothing, the price of a waist trainer is going to vary depending on quality and make of the item.
For example, you can find a great waist trainer for under $50, but if you are looking for a good waist training corset that has steel boning you may have to pay closer to $75-$95 to get a decent quality one.
You may find that some steel boning corsets that work really well for waist training can cost you over $100 and upwards to around $200. Most of these corsets though are custom made and are used not only for waist training but also for costumes or being worn on the outside of your clothing.
Another factor that influences how much you will pay for a waist trainer is the size of the shaper you need. Many times you will find that plus size waist trainers cost more than the small through large size trainers. This is not always the case, but you may run into this with a few different brands that you end up paying a few dollars more if you need a size XXL or larger in the corset.
The cost of a waist trainer will definitely influence your decision on which shaper to buy but you should also keep in mind the quality of the item as well as how much you will be using it as well.
You may be able to find a cheaper waist trainer for only $20 but it may take you wearing the waist cincher twice as long to see any real results due to the lack of quality and structure in the garment. On the other hand, you could pay $45 for a quality made trainer that may help you get results in only a few weeks compared to a few months. In this case it would be worth paying the extra $20 or so for the best waist trainer instead of wasting your time and effort.
When buying a waist trainer you should do your research and compare a few different shapers, but also realize that it may take a few dollars extra to get the type of trainer that will get you that smaller waist and give you the results you want.