Troll Lord Games, the fine makers of Castles & Crusades, have a great sale going on right now and will keep it going as long as folks keep spreading the word (details here: link)
For $20.00 (plus S&H) you can get a copy of the C&C Players Handbook, Monsters & Treasure, and a module (Shadows of Halfling Hall). Normally, all this would cost $56.00. link
Note, these are the hardcover versions of the books. My group (who are recent C&C converts) took advantage and placed a large order.
You only need the PH and the M&T to play, so this is a great starter pack (the Castle Keeper Guide mainly has optional / supplemental rules).
If the combo deal is not up your alley, you can get just the PH for $15 (link) or M&T for $10 (link).