Purchase from bar before time (8)
I believe the answer is:
leverage
'purchase' is the definition.
(I know that purchase can be written as leverage)
'bar before time' is the wordplay.
'bar' becomes 'lever' (lever is a kind of bar).
'before' says to put letters next to each other.
'time' becomes 'age' (an age is a period of time).
'lever'+'age'='LEVERAGE'
'from' acts as a link.
(Other definitions for leverage that I've seen before include "Power to act effectively" , "Economic clout" , "Mechanical advantage; influence" , "financial advantage" , "Strategic advantage; large Eve (anag.)" .)