Tin up the price for the chemical (7)
I believe the answer is:
nitrate
'the chemical' is the definition.
(I've seen this before)
'tin up the price' is the wordplay.
'up' shows that the letters should be reversed in order (in down clue: letters go upwards).
'the price' becomes 'rate' (I've seen this before).
'tin' written backwards gives 'nit'.
'nit'+'rate'='NITRATE'
'for' is the link.
(Other definitions for nitrate that I've seen before include "following 28 [SILVER]" , "Fertilizer" , "salt" , "Tear tin up for fertiliser" , "Natural or synthetic fertiliser" .)