The dress was rather more expensive than I was expecting it would be, so I didn't buy it.

【翻译】这件衣服比我预期的要贵很多，所以我没有买。

疑惑是:

1）进行时表达了什么味道？

——过去进行时：指过去某个时间在做某事。本句指“当时在预期，在期待着”。

2）如何分析这里的句子结构和成分呢？

——The dress was rather more expensive than I was expecting it would be, so I didn't buy it.

总体是个并列句，第一分句是个含有比较从句的复合句。

在这个复合句中，than是“连接代词”，引导比较状语从句，同时作了would be的表语，也就是说，would be后面不能再跟expensive。it would be是expecting的宾语从句。

还有，这句话如何翻译成中文呢？

——已翻译。