It affects sheep, as price is variable (7)
I believe the answer is:
scrapie
'it affects sheep' is the definition.
(I've seen this before)
'as price is variable' is the wordplay.
'is variable' is an anagram indicator (a varied form of the letters).
'as'+'price'='asprice'
'asprice' with letters rearranged gives 'SCRAPIE'.
(Other definitions for scrapie that I've seen before include "Disease of sheep" , "beastly disease" , "sheep killer" , "It affects sheep" .)