Terrible income, so finally choose to save (9)
I believe the answer is:
economise
'save' is the definition.
(I've seen this before)
'terrible income so finally choose' is the wordplay.
'terrible' indicates anagramming the letters.
'finally' suggests the final letters.
The final letter of 'choose' is 'e'.
'income'+'so'='incomeso'
'incomeso' anagrammed gives 'economis'.
'economis'+'e'='ECONOMISE'
'to' acts as a link.
(Other definitions for economise that I've seen before include "Scrimp" , "cut services" , "Make savings" , "save?" , "make cuts" .)