I'd second that $50 estimate. I have never heard that these were any more likely than others for breakage in that area. High mileage, mass-brazed, or furnace-brazed may all break if the braze is not fully completed, or if they get the joint over-cooked. Not a particularly dangerous failure, btw, that bottom bracket break. The bike gets really nice to ride for a little while, and then gradually (if you ignore it) bends toward the ground. Not often catastrophic.