Reduce by ha’pence - ridiculous! (7)
I believe the answer is:
cheapen
'reduce' is the definition.
(I've seen this in another clue)
'ha'pence ridiculous' is the wordplay.
'ridiculous' indicates anagramming the letters.
'hapence' anagrammed gives 'CHEAPEN'.
'by' acts as a link.
(Other definitions for cheapen that I've seen before include "Reduce worth, degrade" , "Tried" , "Depreciate" , "Cut" , "Reduce the price of" .)