There are two unissued stamps of Cochin, which are mentioned and priced in footnotes in Gibbons.
I have this one, the Fifth Raja 1 Anna 3 Pies:

It's currently priced at £225, but it can be found for considerably less than that. This, believe it or not, is uncommon for Cochin. Difficult stamps in this sort of price range will usually sell for up to 100% or more of catalogue value, provided they're in good condition.
Incidentally, for the catalogue cynics who believe catalogue prices never go down, this stamp was first listed in the 1998 Gibbons - at £325.