For about 20 years I've been buying the Makita 4.5" angle grinders that cost about $50-70 at Amazon or the Big Box stores. We have a little herd of them, 6 to 8 at any given time, and we use them fairly hard when we work in metal, but not every day though. Typical lifespan has been 5 to 10 years on a grinder. If you had just one and used it every day, probably not that long... In my experience the bearings go before the brushes do.