£51 is exceptionally dear for a kitchen device (10)
I believe the answer is:
liquidiser
'a kitchen device' is the definition.
(appliance used in the kitchen)
'ps51 is exceptionally dear' is the wordplay.
'psil' becomes 'liquid' (I am not sure about this - if you are sure you should believe this answer much more).
'exceptionally' means one should take alternating letters (alternate letters are excepted or removed).
The alternating letters of 'dear' are 'er'.
'liquid'+'is'+'er'='LIQUIDISER'
'for' acts as a link.
(Other definitions for liquidiser that I've seen before include "Blender" , "Kitchen appliance" .)