Focused study needing minimal money deemed very good (12)
I believe the answer is:
concentrated
'focused' is the definition.
(similar in meaning)
'study needing minimal money deemed very good' is the wordplay.
'study' becomes 'con' (con can informally mean to study).
'needing' means one lot of letters go next to another.
'minimal money' becomes 'cent' (I've seen this in another clue).
'deemed very good' becomes 'rated' (to rate something is to consider it good).
'con'+'cent'+'rated'='CONCENTRATED'
(Another definition for concentrated that I've seen is " Focused - made denser".)