what's the signs for brake replacement?

[acdcfan]

I've done 45k and swapped mine last weekend. they had a good 4-5mm left, when with nightly mountain runs and a few track outings. they were making a horrible noise at slow speeds and was told by the mech I had about 5k left. Honestly they had another 15 with some hard driving included.

How much did you pay?