We are playing Hoard of the Dragon Queen. My PC's are only at level 3. They stumbled into a magic shop and asked for a Bag of Holding. I made the asker roll to beat a 15 and if he did I said that he could buy one. (He rolled a 17.) So then I proceeded to look for for how much one costs in the DMG, PHB & HotDQ. Magic item creation and endless tables were all I found. Someone found a D&D Wiki and said it was 2500 GP. I ended the game (about 15 minutes early) to do my homework. Am I missing something?
My question is:
Why is the Bag of Holding not listed in the Index of any book?
Where do I get price lists for magic items? Or if the answer is "It's at my discretion", what should I use as a guide?