It was there, balancing his checkbook, Max discovered that he and the beautiful Gloria had overdrawn their joint bank account to the tune of 131,465.
この慣用句らしい "to the tune of" を調べます。
・Cambridge Dictionaries Online: to the stated amount: The City Council had financed the new building to the tune of over 4 million pounds.
・Wiktionary: (idiomatic) roughly; about; as much as; to the sum of, to the extent of: The damage that he did to his car was to the tune of two grand
・McGraw-Hill Dictionary of American Idioms and Phrasal Verbs: 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.
用法を知ってしまえばなんて事のない表現でした、と思いかけたら、スラング辞書のUrban Dictionaryに次ぎの様なニュアンスの説明がありました。
Used to mean "approximately", or "in the general range of", but usually only when talking about large sums of money.:
Right Example: So then I had to pay something to the tune of $5,000 for a new one.
Wrong Example: So then I had to pay something to the tune of $0.05 for a new one.
なるほど、引用文の "to the tune of" は131,465も使ってしまったと言うニュアンスがあるようです。