Long ago, when I was a college student, I had a helmet mirror and it was perfect for my needs. For my current bike, Ol’ Paint, I have a mirror mounted low on the front fork. It’s not nearly as effective as my old helmet mirror.
I started searching for mirrors the fit on eyeglasses. (I wear prescription sports glasses with flip-up shades when I ride.) I quickly came across this article on Ice Bike. The Take A Look mirror looks like the bee’s knees, and can be used on either side.
To be fair, it’s not Amazon that’s jacking up the price.