A good one will give the better value for money (7)
I believe the answer is:
tipster
'a good one will give' is the definition.
Although both the answer and definition are singular nouns, I can't see how they can define each other.
'better value for money' is the wordplay.
'better value' becomes 'ster' (I can't explain this - if you can you should believe this answer much more).
'for' means one lot of letters go next to another (I've seen this in other clues).
'money' becomes 'tip' (money given for service).
'ster' after 'tip' is 'TIPSTER'.
'the' is the link.
Can you help me to learn more?
(Other definitions for tipster that I've seen before include "One advising betters" , "Racing tout" , "Supposed expert on horses" , "Adviser on betting" , "Race winner forecaster" .)