Hasten to make the price a dollar higher (4,2)
I believe the answer is:
buck up
'hasten to make the price a' is the definition.
I can't tell whether this defines the answer.
'dollar higher' is the wordplay.
'dollar' becomes 'buck' (slang).
'higher' becomes 'up'.
'buck'+'up'='BUCK UP'
Can you help me to learn more?
(Other definitions for buck up that I've seen before include "Hurry or become more cheerful - like wild horse?" , "Informally become more cheerful or make haste - like restless horse?" , "Take heart" , "Become more cheerful like unruly horse" , "Become more serious" .)