This width thing has been confounding me. So today, I measured my 2012 Prius. In fact, the official width listed in the Prius manual, 68.7", is with NO mirrors! The other dimensions listed - hip room front and rear, shoulder room front and rear, and track - are all about 2" less than the Model 3. So I am going to speculate that the width of the Model 3 WITHOUT ANY MIRRORS is about ~ 71".
I measured my Prius with the mirrors extended and it was 79.8". So adding the same 2" to that figure would make the Model 3 close to 82" with the mirrors extended. So I think the 82.2" figure stated by Tesla is accurate. And that makes the 76.1" figure with mirrors folded equally believable. That means that the folded mirrors stick out about 2.5" to 3" on each side.
The takeaway for me is that the Model 3 is only slightly larger in width than my Prius. The Prius is hardly a large car but with plenty of interior room and I will be happy with the slightly larger size of a Model 3.
A couple of other things I discovered is the Model 3 has about .25" more ground clearance and it is 2" lower in overall height yet the Model 3 has about 1" more headroom front and rear. Finally the Prius has a 0.25 Cd while the TM3 has a 0.23 Cd.