Irritation after second stand becomes most expensive (8)
I believe the answer is:
steepest
'most expensive' is the definition.
(steep can mean very expensive)
'irritation after second stand' is the wordplay.
I cannot really understand how this works, but
'second' could be 's' (common abbreviation) and 's' is found in the answer.
'stand' could be 'tee' (I've seen this before) and 'tee' is found within the answer.
The remaining letters 'pest' 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).
'becomes' acts as a link.
Can you help me to learn more?
(Other definitions for steepest that I've seen before include "Rising most sharply" , "most severe" , "With the sharpest incline" , "Most expensive" , "extremely dear" .)