What is the rarest cockatiel color mutation?

Question

and how mutch is a cinimon cockatiel worth

Answer 1

How much a bird is "worth" is all relative.  How much the MARKET indicates their value is depends on your location and accessibility to breeders.

Cinnamon is a pretty common mutation.  The white face isn't even that rare anymore when only a few years ago it was considered rare.  The problem with Cockatiel mutations is that tiels breed year round and because they are so prolific any new traits that are developed or expressed quickly become common because so many people breed them and in such high numbers.

I would have to say emerald and fallow are still among the rarest mutations, along with yellow cheek, silver and pastels, but then you have to look at combinations of mutations and crossovers as well like a white face cinnamon pearl and other multiple mutations.