I come about imprisoning convict being cost-effective (8)
I believe the answer is:
economic
'cost-effective' is the definition.
(I've seen this in another clue)
'i come about imprisoning convict' is the wordplay.
'about' indicates an anagram.
'imprisoning' indicates putting letters inside.
'convict' becomes 'con' (abbreviation e.g. 'ex-con').
'i'+'come'='icome'
'icome' with letters rearranged gives 'eomic'.
'eomic' enclosing 'con' is 'ECONOMIC'.
'being' acts as a link.
(Other definitions for economic that I've seen before include "viable" , "Fiscal" , "One comic (anag)" , "Using the minimum resources necessary for effectiveness" , "Inexpensive" .)