1
general::
To the sum or extent of, as in They had profits to the tune of about $20 million. This idiom transfers tune, a succession of musical tones, to a succession of figures. [First half of 1700s]
American Heritage Idioms
2
general::
Phrase(s): to the tune of some amount of money
Fig. to a certain amount of money. • My checking account is overdrawn to the tune of $340. • My wallet was stolen, and I’m out to the tune of $70.
McGrawhill's American Idioms And Phrasal Verbs