We have Northern Tool by us and they sell those same trailers as HF. In fact my parents had one years ago that they mounted a cargo carrier to, but they've since given it away.
I've checked out the N/T trailer, $279.99 + sales tax if you bought it in the store, online at the N/T website $259.99 + sales tax and they'll ship free to your home. If you order through ebates.com you can get 1% to 4% back depending if there's a special on. That's for the 12" wheel one, the 8" one is $229.99.