Your workmanship and materials choices both look exquisite! I'm in the $8 - $12 or even $15 camp, depending on the size of the item--it looks more coin purse size, based on the key ring-- which would limit its uses. For the bargain hunters, $10 each or 3 for $25, or $12 each 3/$30.
The button, while a cute accent, is less "user friendly" than a magnetic snap (my own preference), or even velcro, for frequent opening and closing.
Have you considered scaling up the pattern to offer a second size? For more money, of course!