Opposed to increases in a budget, ultimately (7)
I believe the answer is:
against
'opposed to' is the definition.
(thesaurus)
'increases in a budget ultimately' is the wordplay.
'increases' becomes 'gains' (gain is a kind of increase**).
'in' indicates putting letters inside.
'ultimately' says to take the final letters.
The last letter of 'budget' is 't'.
'a'+'t'='at'
'gains' put inside 'at' is 'AGAINST'.
(Other definitions for against that I've seen before include "Opposed" , "close by" , "Con" , "Opposing" , "In conflict with" .)