Ain't nothing but a thing. Assuming there's a C library that would fetch the page, apply the widget, and return the list, it's probably 3-4 days of work.

Using my Markham's Estimating Tool (double the number and go to next higher units) that comes out at 6-8 weeks.

Windows shell extensions are all COM nonsense. You have to know the magic numbers and know where to put them. The rest is pretty straightforward code.