Airway with skill being set up, mostly inexpensive (7)
I believe the answer is:
trachea
'airway' is the definition.
(I've seen this before)
'skill being set up mostly inexpensive' is the wordplay.
'skill' becomes 'art' (I've seen this before).
'being set up' shows that the letters should be reversed in order.
'mostly' means to remove the last letter.
'inexpensive' becomes 'cheap' ('cheap' can be similar in meaning to 'inexpensive').
'art' reversed gives 'tra'.
'cheap' with its final letter taken off is 'chea'.
'tra'+'chea'='TRACHEA'
'with' acts as a link.
(Other definitions for trachea that I've seen before include "Tube taking inhaled air from the larynx" , "get air supply through this" , "Breathing tube" , "The formal windpipe" , "Tube carrying air to the lungs" .)