Price of nuts up -- period (6)
I believe the answer is:
damage
'price' is the definition.
('damage' can be a synonym of 'price')
'nuts up period' is the wordplay.
'nuts' becomes 'mad' (I've seen this in other clues).
'up' says the letters should be written in reverse (in down clue: letters go upwards).
'period' becomes 'age' (I've seen this before**).
'mad' in reverse letter order is 'dam'.
'dam'+'age'='DAMAGE'
'of' is the link.
(Other definitions for damage that I've seen before include "Harm, injury" , "Detrimental effect" , "Physical harm" , "Deface, harm" , "Impair or cause injury to" .)