I've been having a play with SmoothTrack, a new iOS app released yesterday, that provides Head Tracking with only an iPhone/iPad (I think Android is coming, too) and the free OpenTrack software. I got it primarily to try with "that other sim", but I'm happy to say it also works a treat in FS2. It only currently works with certain iPhone models, so check the requirements beforehand.
It's currently half price until the end of the month. I paid £4.99 and it's at least as good as my £85 TrackHat and I don't need to wear a hat or mess with the lights and curtains in the room.
I've no association with the dev, just wanted to spread the word.