Cheapest seats always once included in part of journey (8)
I believe the answer is:
steerage
'cheapest seats' is the definition.
'steerage' can be an answer for 'seats' (I have seen 'Cheap seats' mean 'steerage' so perhaps 'seats' could also mean 'steerage'). I am unsure of the 'cheapest' bit.
'always once included in part of journey' is the wordplay.
'always once' becomes 'eer' (I can't justify this - if you can you should give a lot more credence to this answer).
'included in' indicates putting letters inside.
'part of journey' becomes 'stage' ('stage' is part of 'journey').
'eer' inserted into 'stage' is 'STEERAGE'.
Can you help me to learn more?
(Other definitions for steerage that I've seen before include "Formerly cheapest space on board" , "Cheapest part of liner" , "Cheapest accommodation aboard ship" , "Course" , "Cheapest classes" .)