If it's just the torque member bolt, it threads into the sliding pin. The sliding pin goes across the width of the caliper and has a dust boot on it. Just remove the sliding pin, get a new one at the dealership and a new torque member bolt. A pair of needle nose vise grips usually can grab the sliding pin. If you have to drill anything, get an easy out kit. Drill the hole smaller than the bolt diameter, and use the easy out to remove the broken end. It will save the threads. Without seeing the caliper, I'm assuming thats what you need to know. If it's worse than what you thought, then get a rebuilt caliper with new hardware. But, if you do one caliper, then do the other side too. Don't Mickey Mouse anything with the brakes, do it right.