Ploughman's £50 in bank (6)
I believe the answer is:
tiller
'ploughman's' is the definition.
(I've seen this before)
'ps50 in bank' is the wordplay.
'ps50' becomes 'll' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'in' is an insertion indicator.
'bank' becomes 'tier' (both can mean a row of similar things).
'll' placed within 'tier' is 'TILLER'.
Can you help me to learn more?
(Other definitions for tiller that I've seen before include "Boat's steering handle" , "Steering lever" , "Lever to turn the rudder on a boat" , "Farmer" , "Rudder's steering handle" .)