元を取る (moto wo toru) means “get your money’s worth”, i.e. “get what is worth the money you have paid”. For instance, if you’re studying at university, you probably want to 元を取る by making the most of the opportunities and absorb as much knowledge and experience as what is worth the tuition fees.
In particular, this idiom is often used when people go to an all-you-can-drink/eat restaurant and try to get what is worth the cost by eating/drinking food/drinks that you think would be the most expensive on the menu. For instance, at an all-you-can-drink izakaya, some people keep drinking beer only and do not care about the other drinks such as cocktails (e.g. lemon sour), because those izakaya drinks are often diluted very much and their cost is generally much cheaper than beer. Some people are too obsessed with 元を取る and prioritise this goal over the original intent, that is, to enjoy the meals/drinks – if you eat/drink too much and feel very sick as a result of trying to get your money’s worth, that is 本末転倒 (ほんまつてんとう), a Japanese cool four-kanji word meaning “primary objectives are sidelined/overshadowed by secondary objectives”.
See also: Meaning of 本末転倒
割(わ)りに合(あ)わない “not worth it”
コスパが良(い)い/悪(わる)い “good/bad cost performance”