I think its worth testing your alternator, before going to such expense, by disconecting the harness closest to the alternator and checking the output directly.
The photos are from the D10 workshop manual. Dont worry about the test rig they talk about just use a multimeter set on AC volts. You will then get some idea as to whether the fault is at the alternator or further up the wiring harness.
You can also check the resistance of the alternator coils because, helpfully, the manual gives figures. I would check that with the stator off the bike to avoid putting any current through it which could damage the magnetism of the rotor.
If you get output at stator then suspect the harness, the switches( especially if they are old. They do corrode up inside) and the rectifier.