During a ride today, one of the spokes in my rear tire broke. It broke near the nipple and I will take it to the LBS tomorrow. My question is how did it break? I didn't hit a pothole, it doesn't appear to be rusted, the wheel is a few years old but I've had bikes with older wheels and this has never happened before.

Also, what should I expect from the LBS in regards to cost and possible up sell? Can they just replace the broken spoke or will every spoke have to be replaced? I assume I will need to get the wheel trued as well.

Thanks in advance.