Look. I'm not flaming you, honest. I really, really, really want to help you out here, but you're not making it easy. You need to tell people where you are. I hate to tell you, but if you're in New York, and someone builds it for you in California, your $14.50 price is out the window. Check
here. If you put in different Zip Codes, the price changes. Also, don't forget you're working with larger dimensions, which changes the price. I put in New York to New York, at 15lbs, and 24"x12"x4", and it gave me around the $14.50. When I put in the same digits to California, it changed to over $30.
As CheffoJeffo said, please provide a bit more information...