For each issue, one pound for an ad (8)
I believe the answer is:
personal
'an ad' is the definition.
(personal ad is a type of advert)
'for each issue one pound' is the wordplay.
'for each' becomes 'per' (I've seen this before).
'issue' becomes 'son' (issue can mean someone's offspring).
'one' becomes 'a'.
'pound' becomes 'l'.
'per'+'son'+'a'+'l'='PERSONAL'
'for' is the link.
(Other definitions for personal that I've seen before include "Relating to the individual" , "Pertaining to the self" , "Such a rude remark" , "Pertaining to oneself" , "Confidential" .)