Probably very similar to the temperatures anywhere else on Mercury's surface - with no atmosphere, temperature doesn't vary much with altitude. So, somewhere around 500-700K during the (3-4-month-long) daytime, and around 100K at night.
"Because the crater is deep, and the Sun never gets very high off the horizon at the pole, there are parts of the crater floor that are permanently in shadow; they literally are never illuminated by the Sun. Those spots can be very cold; well below the freezing point of water" from this article http://www.slate.com/blogs/bad_astronomy/2012/11/29/_mercury...
