I used to use public transport a lot, espcially when I was working in Shanghai.

In the original sentence you had two tenses:

First: "I use public transport a lot," is continuous tense: (Yesterday, today and probably tomorrow) I use public transport a lot.
Second: "especially when I was working in Shanghai." is past tense (was): I used public transport a lot when I was in Shanghai.

In English the tense is the same within one sentence.

So you can make two sentences:
I use public transport a lot. I used it even more when I was working in Shanghai.

Or you can make the tenses the same:
I use public transport a lot, especially when I'm working in Shanghai.
I used public transport a lot, especially when I was working in Shanghai.

Looking at your other sentences it seems like you are thinking about the difference between your past (using public transport in Shanghai) and your present (driving in your hometown).

So I think you want to say: I used to use public transport a lot when I was working in Shanghai.

The metro and buses in Shanghai are very cheap, usually costing 2 to 5 RMB, which is about 0.30 to 0.7 dollars70 cents US.

We don't use percentages to refer to dollars. It changes to cents.

I think here you are referring to your time in Shanghai.

And there are a lot of stations in the city, making public transportation very accsessible.

Spelling of accessible.

I used to use public transport a lot, especially when I was working in Shanghai.

Your last sentence makes it sound like you don't use public transport much anymore, so I changed this to past tense.

The metro and buses are very cheap, usually costing 2 to 5 RMB, which is about 0.3 to 0.7 dollars.

You could specify that you mean USD here.

And there are a lot of stations in the city, making public transportation very accsessible.