In recent years the budget carrier has softened its no-frills image: in 2014 it introduced business fares, for which passengers enjoy priority boarding and a little more legroom.

【翻译】近年来，廉价航空公司已改善了其只提供最基本服务的形象：它在2014年推出了商务舱票价，凭此价乘客能享受到优先登机和更宽敞些的腿部活动舱位。

【分析】for which passengers enjoy priority boarding and a little more legroom为定语从句，修饰fares（票价），which 指代fares，介词for 提到了关系代词之前。for 的意思是“付出”，表示支付这个价格就可以怎样。