Technically speaking, a "flipper" is a subset, or type, of partial denture
. So, your question becomes an issue of semantics, and how you define the terms "partial plate" or "partial denture" and "flipper.
The way it is usually defined, a "flipper" is a removable partial denture that usually contains one, or at most a few teeth that is retained in the mouth solely by means of an acrylic extension or base. It is a partial denture in its simplest form, and consists of only two components-- the tooth itself, and a small extension that can be called a base, saddle, or palate, depending on its design and whether it's an upper or lower flipper.
On the other hand, the term "partial denture" may be applied to a wide variety of prosthetic devices, and may consist of a wide array of components-- clasps, semi-precision attachments, precision attachments, interlocks, stress-breakers, minor connectors, major connectors, and any combination of one or more teeth (it would not include ALL the teeth, because then it would be designated as a "complete denture
So, the cost of a denture is directly related to its complexity, and a flipper is the simplest and least expensive partial denture that can be made.
Hope this helps...