but it costs almost three times as much.这个中间是不是省略了什么?这个as much是什么用法?

没错,是省略了一部分句子成分.
例：但是节假日的房价比平常要高三倍.
but it costs almost three times as much as normal.
as much as 和...一样多
和平时的三倍一样多
与adj-er一样,它也是比较的一种表达方式.