Lauder mascara's top value (6)
I believe the answer is:
esteem
'value' is the definition.
(I know that value can be written as esteem)
'lauder mascara's top' is the wordplay.
'lauder' becomes 'estee' (I've seen this before).
'top' suggests taking the first letters (in a down clue, the first letter is top).
The initial letter of 'mascaras' is 'm'.
'estee'+'m'='ESTEEM'
(Other definitions for esteem that I've seen before include "Floor covering" , "Favourable regard" , "Think well of" , "Honour - regard" , "Hold in deference and respect" .)