One of my co-workers - who rides down to about 15/20 F and wears glasses - turned me on to a cheap and moderately effective solution. She just ties a bandana around her nose and mouth, and it works reasonably well to block wind and keep some of the hot air from going up.

I've tried a version of the bandanna trick around 0F. I tied the bandana, then put my ski goggles (cheap single lens variety) just barely touching the top, then put the face part of the balaclava loosely over the bandana. Even breathing heavily at stoplights, there was significantly less fog.

I would not endorse this solution for seriously cold weather, as the cotton bandana gets very wet. I'm currently in the market for a large scrap of wool.