ご指名質問（回答）:pay out of (one’s) pocket

Jakieさんからのご指名質問にお答えします。

既にJakieさんも言及していましたがpocketには「（洋服・鞄などの）ポケット」とは別の語義があり、ここでは「（金銭を入れるところとしての）ポケット；所持金；収入、資力」（『ジーニアス英和辞典　第３版』大修館）の意になります。

それらを踏まえた上で、辞書に当たって見ますと、通常pay out of (one’s) pocketという形で用いられ「自腹を切って払う」（ibid）という定義になります。英英辞典にも次のように記載されていました。’ (of an expense or cost) paid for directly rather than being put on account or charged to some other person or organization.’Oxford Dictionaries Online (Shou-VR*)

Teachers pay more out of pocket for their students

A second-year pre-kindergarten teacher at Salem Elementary School in Apex, N.C., Hannah Martin makes about $34,000 a year and in her spare time takes as many babysitting jobs as she can get.
Martin, who rents a room in a house she shares with four other women, said the work outside her classroom is necessary if her students are to have the school supplies they need.

http://www.nbcnews.com/business/teachers-pay-more-out-pocket-their-students-6C10913899