At this budget, there isn’t really a true “digital AE-1” with all of your requirements. The closest match in concept is a rangefinder-style camera, which is why used options like the Leica M8 or Epson R-D1 were suggested.

The main trade-off is the viewfinder: if you want interchangeable lenses and a compact body for much less than an M9, you’ll likely need to accept an electronic viewfinder rather than a large optical/rangefinder finder. A good EVF can still work well for manual focus and is often better than the small tunnel-style finders on many compact cameras.

The Fujifilm X100 is appealing for size and shooting style, but it does not have interchangeable lenses, so it doesn’t fully meet your brief.

So the realistic options are:

• used Leica M8 or Epson R-D1 if you specifically want that rangefinder-like experience
• otherwise, accept an EVF-based compact interchangeable-lens camera as the practical compromise

If your priority is street photography with manual-focus-friendly handling, the used M8/R-D1 route is the closest fit among the options mentioned.