I too would be interested in a space saver spare wheel. It was the first thing I bought when I got my last car, a SEAT Leon. I sourced one from a MKV Golf for only £25 and just replaced the whole fitting in the car boot.
Does the Prius not have a space saver that would fit the CT200? If not, is it possible to just purchase a Lexus wheel and tyre without any other parts?
Gerry