Alright so lets say I have access to a Caster at 10th level who has all the right feats and so forth and makes a Ring or Something of the spell Book Ward, which is a level 2 spell.
Book Ward
It says it acts as Protection from Energy except only against fire AND acid not Fire or Acid which leads me to believe it should be both at one time.
Now the questions are
1. Am I reading that right that it is both, not one or the other?
2. How much would say a ring of continuous use cost me? And because it says a touched object, would clothing count?
So, because of the wording it firstly functions like Protection from Energy. Which means it can only protect against one energy type per casting, with the additional restriction of only being able to provide protection against fire and acid, not cold or lightning.
Of course, I don't like such a literally interpretation and the way the rest of the spell is written I think it's supposed to gain the effects as if Protection from Energy were cast twice on the object. One for fire, and once for acid.
A ring of continuous use wouldn't help you much, because it can only protect objects. While it might protect your clothing, that protection wouldn't extend to you at all. Further pricing cutom magical items is something you should discuss with your GM to find out what they think is appropriate.