你曾经帮他们做过项目，按照你通常的费用。

You've done work for them before, at your usual rates.

youdao

这通常没有防潮布，虽然会产生额外的费用，但是你可以买一个跟它配套。

This doesn't usually have a groundsheet but you can buy one to fit, though it costs extra.

youdao

相反，他们会得到固定的费用，通常一节标准四小时声乐课的费用是825美元。

Instead, they receive a fixed rate, which is typically about $825 for a standard four-hour vocal session.

youdao