Today most chips are only available in SMD packages, therefore I often need adapter boards for prototyping. There are only a few manufacturer of adapter boards and they are often very expensive. I think the reason for the high price is, because most of this boards are made to replace DIL chips in devices with SMD ones. So this boards require a certain quality for this productive use.
For prototyping this is not my greatest concern. In most cases I am happy to get chips working and be able to experiment with them. I am aware there are many limitations on a breadboard, so the adapters do not have to be electrical perfect for my use. Spending $6-$9 per adapter, often for a single use, for a chip which costs only a few cents seems wrong to me.
Now I discovered, Adafruit has a nice set of SMD adapter boards in their shop. You always buy a set of three, six or even more, and they have different package sizes on both sides. It is exactly what I would expect from an adapter board for prototyping.