a drop in the ocean 沧海一粟；九牛一毛

【例句】
His fee is a drop in the ocean compared with the real cost of broadcasting.
同播出的实际开支相比较，他那点酬金不过是九牛一毛。

By comparison with North Sea oil production, it is a drop in the ocean.
与北海的石油产量相比，这只是沧海一粟。