Guide regularly argues for cheapest class (8)
I believe the answer is:
steerage
'cheapest class' is the definition.
(cheapest accommodation on a boat)
'guide regularly argues' is the wordplay.
'guide' becomes 'steer' (synonyms).
'regularly' indicates alternate letters (regularly take one letter, leave next etc.).
The alternating letters of 'argues' are 'age'.
'steer'+'age'='STEERAGE'
'for' acts as a link.
(Other definitions for steerage that I've seen before include "The cheapest fares" , "Densely-packed travellers here" , "government" , "Cheapest accommodation aboard ship" , "Formerly cheapest space on board" .)