Inexpensive treats are already available in the single-digit euro range. Most are products with simple ingredients, which can often be chemically supplemented. Organic products or those with exotic meat naturally cost more. Of course, the price depends not only on the quality but also on the quantity. It is not uncommon to get a discount for larger order quantities.
However, when considering the price, always bear in mind that some treats, such as chew bones, have a longer "shelf life" or "usability", as they are not eaten in one piece, but are chewed over a longer period of time and wear out over time.