If your still looking for help, here is a general rule to doing it yourself if you have never tapped a broken bolt before.
If you have a good view of the broken bolt you can do it. What this means is that you need to have the room to be able to look straight in on the bolt. This is important becauce you will need room for your tools to work straight and centered.
NOW: What a reverse tap does. You pre-drill a small guide hole dead center of the broken bolt. Then, the tap is "simular" to a drill bit; but, with reversed threads. This allows the tap to bit in, Not cut into, the bolt. Once it grabs on, it will spin the bolt out. It must be centered and you CANNOT use force (ie. a drill or force on a socket) to tap it out. Either with a very slow turn on a socket, or even better a small handheld wrench, turn the tap.
Two warnings:
If you don't have the room and angle to tap the bolt staight and centered, let someone with experience do it for you. Even if you have to pay, it is worth it.
And, really important, when purchasing a reverse tap, expensive is better. It will be the difference between about three dollars and 15 dollars. I know, because I grew up tapping bolts on farm trucks and equipment. Last week I had to tap a bolt on my ti that holds down the valve cover. I just went down to the local auto shop and bought a cheap tap thinking this would be an easy job because the bolt broke while I was putting it in; hence, no freezing/ sticking problem. WRONG ANSWER. The tip of the tap snapped off
and I swear it looked like it was made from pot metal. What a disappointment. A quality tap will save you a lot of hassle.
Red
'95 318Ti