Heard successor getting reasonable cost of flying (7)
I believe the answer is:
airfare
'cost of flying' is the definition.
(fare or price for air travel)
'heard successor getting reasonable' is the wordplay.
'heard' shows a homophone (sound like).
'successor' becomes 'heir' (synonyms).
'getting' says to put letters next to each other.
'reasonable' becomes 'fare' (I can't explain this - if you can you should believe this answer much more).
'heir' sounds like 'air'.
'air'+'fare'='AIRFARE'
Can you help me to learn more?
(Other definitions for airfare that I've seen before include "Price of flying" , "Money for a flight" , "Charge for flight" , "Fee for a flight" , "Cost of a flight" .)