The key difference is the brush material, as others have noted. Synthetics are cheaper, but you've already noticed the downside. Sable is a natural hair, and will stand up much better with some care. Don't get sold on "red sable"; it's just a marketing ploy for synthetics. I still manage to beat up my main brushes, but when I'm painting a lot, that ends up being a cost of doing the work. I reserve my top-quality brushes for fine work, and they're still sharp after 5+ years.