你们需要多少数量? 用英语怎么说？

How much do you need? 及 How many do you need? 都可以，视乎所指的东西是可数还是不可数的，可数的用How many， 不可数用How much。

This is the lowest price. It can't be lower any more.

HOW MUCH DO YOU WANT?(看这个东西可不可数，可数的用MANY)
IT'S THE LOWEST PRICE.

How many do you want?

it is the lowest price.

HOw much do you have?

How many do you want?
This is the lowest price,there's no discount.