How big? $300 isn't going to buy much of a toolbox, if you are looking for both top and bottom.
EDIT: I found this @ Harbour Freights' website, I have absolutely no idea as to the quality, but it is in your price range. I have never seen one of these, or been to a harbour freight, as we don't have them in Canada, but picked it because you may have one near you.
link to the page: Tool box set for $350.00