The Ferret Nation and Critter Nations are pretty much the best you can buy right now. One great thing about them is you if you can't afford a double right away you can actually buy a single unit now, and then save up for an add-on later.
Critter Nation single unit it's not under $150 on amazon though. They do go on sale from time to time though. I also know people have had luck checking classifieds for used ones, they are really sturdy cages so if cared for they can last decades. Most other cheaper ones you might get a few years out of before needing a new one.