As professional systems like TrackIR are prohibitively expensive, especially considering what they are, I decided to try to make my own IR headtracker for cheap. I have succeeded and I am so amazingly happy with the result. It was very easy and cost me less than 30 dollars. I used as much as I could from around the house:
IR LEDs from old remotes and a broken AirHog toy
Popsicle sticks glued together with a glue gun for a clip
The IR filter off a broken WII remote to filter natural light for my laptops webcam (just taped it in place so i can remove it when necessary)
The software I used is a free program called Opentrack.
There are many good websites that give you all the info you require if you google DIY IR headtracker.
If you cant afford a professional setup, I urge you to try it yourself. It works and it saved me hundreds of dollars.