The cheapest way is to replace the Voltage Regulator in back of the alternator.
There are a few 'copies' of OE out there, so get a known brand like Bosch.
It is real easy to swap out, two Phillips or slotted head screws and roll out the Reg'...no wires to mess with.
New one is harder to install due to longer brushes.
Roll it in and forward and locate it with both screws before you tighten them up.
You might pull the ground off the battery to be real sure you don't weld the screwdriver to the Alt Batt+ post.
The old Reg will usually have very short worn out brushes. They don't sweep the charge off the rings and you get your classic fuzzy light symptoms.
'corse....this could be all wrong, but hey !
Waddaya want fer free !
Hells bells....this piggin' post is 4 months old !!!!