A steep change in old money (6)
I believe the answer is:
peseta
'old money' is the definition.
(I've seen this before)
'a steep change' is the wordplay.
'change' indicates an anagram.
'a'+'steep'='asteep'
'asteep' with letters rearranged gives 'PESETA'.
'in' is the link.
(Other definitions for peseta that I've seen before include "Obsolete coin" , "Old Spanish currency" , "Spanish bread once" , "Pre-euro money unit in Spain" , "Former Spanish coin" .)