Used price: $9.50
Buy one from zShops for: $10.27
We've been using this book for two years. During that time it has been an invaluable reference for our collection. Any time we suspect something may be wrong with one of our snakes, the very first thing we do is consult this book. If the problem is included (and it usually is), there will be a chapter outlining what the possible causes might be and what we can do to help prevent it or correct it. It also helps us figure out when we need to take the animal to a veterinarian -- and, for that matter, when we don't, and can look after the situation by ourselves.
But its real value is showing you how to keep your snake healthy and prevent medical conditions from arising in the first place. That means fewer snake deaths and fewer expensive trips to the vet, which makes this book an excellent investment. If you keep snakes, buy it if you don't already own a copy -- you owe it to them.
If you like snakes and live in the eastern US, buy it. If you like snakes and live in the western US, buy volume II (which seems to be just as good, if not better, but I have not actually tried any of the information in.) If you love snakes and live anywhere in the world, buy both of them.