Price is reasonable, say (4)
I believe the answer is:
fare
'price' is the definition.
(I have seen 'Price of passage ' mean 'fare' so perhaps 'price' could also mean 'fare')
'reasonable say' is the wordplay.
'reasonable' becomes 'fair' (associated in meaning).
'say' shows a homophone (sound like).
'fair' is a homophone of 'FARE'.
'is' acts as a link.
(Other definitions for fare that I've seen before include "Food, or price of bus ticket" , "Payment for journey" , "Range of food; travel" , "going rate?" , "Transport charge" .)