whatever you do don't buy another alternator unless the one you currently have no longer works, if you can pull it out of the vehicle and test it individually from canadian tire or wherever you parts guys test there products, 4 in one year is absurd, an alternator will last more than 2 years and most manufacturers have a 2 year warrenty, it sounds like a wiring problem, or a bad battery. your car probably has an internal voltage regulator(inside the alternator which has to be replaced as an assembly... not always but it's usually the same cost as getting a new alternator) so unless your buying junkyard used alternators then you shouldn't be having any problem with your new alternator. i would say bad wiring, corroded or loose connections, or your b/f royally f-ed up the speaker job. but it shouldn't be going thru alternators like that so find a good mechanic and have em take a look.
Despite the high cost of living, it remains very popular.