£6 (not 9) for seafood (5)
I believe the answer is:
squid
'for seafood' is the definition.
(squid is a kind of seafood)
I don't understand how the rest of the clue works.
(Other definitions for squid that I've seen before include "Eight-armed mollusc" , "Calamari" , "Catch" , "Sea creature" , "Large cephalopod" .)