at sb's expense 的字面意思是“自己花钱”“自费”。如:
She traveled at her own expense to Russia. 她自费去俄罗斯旅行。
He had copies of the book printed at his own expense. 他自己花钱印了这本书。
We were supposed to provide safety equipment at our own expense. 我们必须自己掏腰包购买安全设备。
Teachers who signed up did so out of personal choice and at their own expense. 报名的教师完全出于自愿而且费用自理。
The tour is free, but all meals are at your own expense. [=you must pay for your meals] 本次旅行免费,但所有餐费自理。
根据你的句子语境,将其翻译成“牺牲自己的利益”是合适的。