Easy, is it? Well, not for Amazon:
Look, I know the economy is bad and the US Dollar sucks, but if we just look at the numbers, then 22.50 is bigger than 15, is it?
Oh, wait, actually it is listed as less than $15 because one of your third party sellers of Amazon's Marketplace has it:
Amazon, why do you have a filter for "Seller: Amazon.com" only to ignore it then? But let's look at the $13.69 offer:
Wow, so you got some shitty seller with 50% positive ratings that charges $15 for shipping a product that weighs a mere ounces from Texas to California and you think that this offer is so good it should be in my search results for "Prime Eligible" (=NO shipping Costs) and "Seller: Amazon.com" (=NO third party vendors)?
Inflating shipping costs to undercut the competition on the product price while still making a decent profit is the oldest trick in the book, even eBay reacted to it and is now sorting their auctions by "Price + Shipping Cost", and yet your crappy search isn't smart enough to do that?
If you need an Engineer to fix your shitty search in his spare time, drop me an email and I'm sure we can arrange a little side-contract for less than a $100k. And don't tell me that's not worth it, after all you're the company that came up with the "Milliseconds equals money" equation - and if each millisecond is costing you a truckload of money, how much money is your shitty broken search costing you?