It seems, sir, that a cuppa is costly on the Continent! (7)
I believe the answer is:
teacher
'it seems sir that a' is the definition.
The definition suggests a singular noun which matches the answer.
'cuppa is costly on the continent' is the wordplay.
I cannot really understand how this works, but
'cuppa' could be 'tea' (informal term for a cup of tea) and 'tea' is found in the answer.
The remaining letters 'cher' is a valid word which might be clued in a way I don't see.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for teacher that I've seen before include "School educator" , "supply?" , "Cheater (anag.)" , "One who educates" , "Lecturer" .)