Archaeological publishers Oxbow Books have lots of bargains for sale on their website and in their printed Bargain Catalogue 2009 (available from them by post).
From the former:
Astrology in Medieval Manuscripts by Sophie Page.
Assesses the role of astrology in medieval society as a
whole, in agriculture, politics, medicine, weather
forecasting, cosmology and alchemy, accompanied by
many lovely illustrations. 64p, many col pls (British
Library 2002) Pb was £7.95 now £3.95