By arrangement, puts up about a third of the fee (5)

'by arrangement' is the definition.
'setup' can be an answer for 'arrangement' (thesaurus). I'm not certain of the 'by' bit.

'puts up about a third of the fee' is the wordplay.
'up' says the letters should be written in reverse (in down clue: letters go upwards).
'about' indicates putting letters inside.
'a third of the fee' becomes 'e' (I can't justify this - if you can you should give a lot more credence to this answer).
'puts' backwards is 'stup'.
'stup' enclosing 'e' is 'SETUP'.

Can you help me to learn more?