I have "rebuilt" alternators before when the problem is brushes or regulator or a bad diode trio, takes about 20 minutes. In general I do not mess with bad bearings since I do not have a press.
Have also done some "mixing and matching" of stators and armatures to create a usable alternator from parts, is how different amp ratings are derived.
In general, a higher amp alternator may have a lower output at idle than a lower peak rated one of the same design, is why alternators are usually matched to the requirement.
For the family cars though I generally buy something with a lifetime guarentee.