Calculate price per unit
Unit cost (cost per item).
I realize this may be super tricky, but maybe AI pattern recognition can solve it. Being able to browse products that have quantities and be automatically shown the $/unit would be a seriously cool feature. Indeed Bing should implement the concept on searches returning shopping results.
Here's a place to start for contemplating purposes: Search on target.com for "ping pong balls". The search result is a manageable number of offerings with a wide range of prices and quantities per package.