Revision of the law ultimately costly for rich (7)
I believe the answer is:
wealthy
'rich' is the definition.
('wealthy' can be similar in meaning to 'rich')
'revision of the law ultimately costly' is the wordplay.
'revision of' is an anagram indicator.
'ultimately' says to take the final letters.
The last letter of 'costly' is 'y'.
'the'+'law'='thelaw'
'thelaw' with letters rearranged gives 'wealth'.
'wealth'+'y'='WEALTHY'
'for' is the link.
(Other definitions for wealthy that I've seen before include "Affluent" , "Rich and prosperous" .)