Hello, I did a lot of data mining/scraping projects before, and I finished amazon scraping project just recently. Customer was fully satisfied, and I gained experience with amazon's site page structure.
I can automate your task with windows desktop application (.exe) with simple GUI. I guess it will have some checkboxlist where you can select one or many top-level categories, than the application will dig subcategories as you suggested. I can use Delphi programming laguage, its advantage is that finished application wont require any additional software installed (like .NET framework or Java VM).