I've never been in this situation, but I'm curious about what the best way to handle it would be.
When I go to the movies, I never pay to see 3D movies for a simple reason. I wear glasses, which means I have to wear the 3D glasses on top of my regular ones. This never works very well and if I so much as tilt my head slightly, the 3D glasses fall off. I have to sit straight up, perfectly still, and even then, something about the double glasses makes the 3D effects look rather wonky (things look very hazy + double vision). If I take off my regular glasses, my vision is fuzzy. Essentially, I can't enjoy a 3D movies, so I opt not to see them. Why pay $5 extra on top of a $10 movie ticket for a less-enjoyable experience? DH doesn't particularly care for 3D movies regardless.
What we do if we went to the movies with friends who DO want to see the movie in 3D? Are they supposed to "downgrade" to the regular movie since I can't comfortably watch the 3D version? If it was the same price as a regular ticket, I might be willing to suck it up and go, but I am not okay with paying extra for a feature that actually degrades the experience for me. Do I suck it up and pay for the 3D? Do friends pay the price difference for my ticket?
The obvious answer is to simply not see the movie with friends who want to see 3D, but I'm curious what would be the next-best option would be.