Price and label are changed becoming priceless (13)
I believe the answer is:
irreplaceable
'priceless' is the definition.
(thesaurus)
'price and label are changed' is the wordplay.
'and' is a charade indicator (letters next to each other).
'changed' indicates anagramming the letters.
'price'+'label'+'are'='pricelabelare'
'pricelabelare' with letters rearranged gives 'IRREPLACEABLE'.
'becoming' is the link.
(Other definitions for irreplaceable that I've seen before include "Cannot be substituted" , "precious!" , "Without possible substitute" , "Impossible to substitute for" , "Whose loss cannot be made good" .)