It's not also so much the rebuild itself, it is the install. I don't know if all the Focus's are the same. But a lift comes in handy when having to access the alternator, plus putting the belt back on.
On 10/2010 at roughly 50K. I had to replace mine plus parts. The alternator, idler pulley, and pulley was $345. My Mechanic does not go to Autozone, I am pretty sure he buys from NAPA with the exception of Ford only if necessary.
What I do know, is the parts are of good quality, I never have to go back and have it done again unless it is a defect within the car. And doing my research, the 07 Focus has a less than reliable electrical system.
At any rate, it cost me a painful $500 to replace it. Unfortunately with today's cars. They may be built better, but some us do not have the capacity or resources to fix them ourselves.