Welcome to United Bimmer.
The ticking noise is usually caused by the lifters after being starved of oil, or sitting for a long time. The noise can go away with proper oil changes, and usually adding an extra half quart.
Check your oil, if it is milky brown it means coolant has mixed. If your coolant is disappearing and their is no visible signs of leaks, then i hate to say it but your headgasket is probably blown. A compression test would tell you for sure.
The gasket itself is $74US, but its the labour that makes it a pain. If the car has overheated you have to send the Head off to be machined and planned and inspected for cracks or stress fractures. It takes less then a day to remove the head off the engine though. But putting it back and ensuring the timing is correct is what takes longer. This is why the repair is fairly expensive.