The best way to grab JSON data from website and put it in CSV?

I tagged this question as “conceptual” because I’m not sure if creating Chrome Extension is the best way. In my opinion it’s better to ask before spending few hours writing something and find out that some part is too much difficult or impossible.

The problem
I used to analyze my finance using csv files downloaded from bank account. But as it sometimes happens, my bank launched new GUI and csv feature disappeared. They do not know when and whether they will do it at all. So I have to grab transactions in some way and put them in CSV file.

Concept of solution
I think scrapping the page with transactions it’s not good way, because whole data is looking like generated with totally random CSS classes and ids. I noticed that list of transactions is sent in JSON format by AJAX response. I analyzed that JSON and every interested field has name, so access to data is quite easy. Only one problem I see, it’s that first JSON load shows only first 10 transactions. To load more I have to scroll down, then there is next AJAX request to the same URI, then next JSON load comes in response. So, if I want to get transactions from whole month I have to scroll few times down and my tool should catch first and also next responses.
I don’t have experience with Chrome Extensions but they claim that if I know web technologies like JS, CSS, HTML it shouldn’t be difficult to write simple extension. If I can take this JSON from AJAX response to my extension then generating CSV file shouldn’t be problem.

The question
The main question is if my concept is possible to realize. Is there easy access to data loaded from AJAX response? If you see any better solution I’m open to suggestions.