The reason why some types of epoxy cost more than others is because of the amounts of solids. The higher the solids count, or volume, the fewer additives and water there is. For example, cheap paint kits with resin are far less expensive than 100% solids epoxy. The finished result also speaks for itself, revealing its true quality.
Higher solids products also require professional tools and equipment to handle correctly. Otherwise, you will only have an expensive mess to clean, and an unfinished floor. Other types rely on chips, flakes, paint chips, and other decorative add-ons. Water-based epoxy, on the other hand, is more affordable as it has fewer solids present.