Professional who translates art into price (12)
I believe the answer is:
practitioner
'professional' is the definition.
(I know that practitioner is a type of professional)
'translates art into price' is the wordplay.
'translates' is an anagram indicator (I've seen 'translated' mean this).
'art'+'into'+'price'='artintoprice'
'artintoprice' anagrammed gives 'PRACTITIONER'.
'who' acts as a link.
(Other definitions for practitioner that I've seen before include "One involved in medicine, such as a GP" , "Person actively involved in a profession (especially medicine)" , "Professional person, esp. doctor" , "Trained professional" .)