MO 307.170.4. Mirrors: All motor vehicles which are so constructed or loaded that the operator cannot see the road behind such vehicle by looking back or around the side of such vehicle shall be equipped with a mirror so adjusted as to reveal the road behind and be visible from the operator's seat.
Missouri's code doesn't have specific rules (basically, a mirror has to provide a clear view of the area behind the car), but in most states, there must be a minimum of one outside mirror. Many small vehicles came several years without a passenger side mirror (except as an option) such as the Ford Festiva, the Geo Metro, and the Honda Insight.
I followed others before me from ecomodder and fashioned some interior mirrors using homemade brackets and convex "blind spot" mirrors.
I found a great solution to having an outside mirror as well. Even though it's not required by law, I'm sure lots of police officers will think they know otherwise. I don't want to get hassled unnecessarily, so I used a really neat wedge-shaped convex mirror designed to be stuck under large SUV mirrors. It came in a two-pack for $8 at O'Reilly Auto Parts. Here are some photos - with the "baby mirror" and no passenger mirror, I removed over two square feet of frontal area.
I also finished the grill block wraparound and I decided while I was at it I'd continue it to make a partial wheel skirt. It looks pretty good - hard to notice except for the off-green color in my opinion.