Always goes in coach – it offers cheapest fares (8)
I believe the answer is:
steerage
'it offers cheapest fares' is the definition.
(historically, cheapest accommodation on a ship)
'always goes in coach' is the wordplay.
'always' becomes 'eer' (poetic way of saying ever).
'goes in' is an insertion indicator.
'coach' becomes 'stage' (stagecoach).
'eer' put inside 'stage' is 'STEERAGE'.
(Other definitions for steerage that I've seen before include "It's the cheapest way to go by sea" , "Cheapest accommodation in old passenger ships" , "Cheapest part of passenger ship" , "Cheapest part of liner" , "government" .)