Ancient city grasping a way of buying up prize (6)
I believe the answer is:
trophy
'prize' is the definition.
(synonyms)
'ancient city grasping a way of buying up' is the wordplay.
'ancient city' becomes 'troy' (Troy was an ancient city).
'grasping' means one lot of letters goes inside another.
'a way of buying' becomes 'HP' (abbreviation for hire purchase).
'up' says the letters should be written backwards (in down clue: letters go upwards).
'hp' reversed gives 'ph'.
'troy' placed around 'ph' is 'TROPHY'.
(Other definitions for trophy that I've seen before include "Prize symbolising victory" , "Memento of success" , "Prize of war" , "Victor's prize" , "Object symbolising success" .)