Thule and Yakima are the largest brands in the US. You can often pick up used racks on craigslist for very cheap. For a bare roof car, you will probably end up needing to still buy the specific adapter mounts for your car, but the rest (base feet, crossbars, mounts such as bike or ski racks) can be bought used fairly easily.
Or, for new, take a look at etrailer.com. They carry some other brands too that are cheaper, but still sturdy and quality, like Rhino and Inno.