At a certain cost, there's a slim chance of improving it (6)
I believe the answer is:
figure
'at' is the definition.
The definition and answer can be both quantities as well as being singular nouns.
Perhaps there's an association between them I don't understand?
I don't understand how the rest of the clue works.
Can you help me to learn more?
(Other definitions for figure that I've seen before include "Consider" , "Shape; amount of money" , "Work out" , "form" , "Imagine; integer" .)