You don't actually need a full face motorcycle helmet, that's overkill for cycling speeds (and uncomfortable with exertion). I regularly commute to work by bike and after a bad fall where I almost landed on my face, I decided to upgrade from a normal helmet to a full face bicycle helmet. You can get a decent one for ~$150 and it'll give you some protection even if you fall flat on your face. Highly recommend as a normal helmet doesn't do much for your face and a lot of falls could result in facial damage.