So poking around a little, I determined that there are really only two types of coffee roasters: hot drums (you put the beans in the drum and they get tumbled or stirred as the drum heats up) and fluid bed (hot air, just like a popper). Cheaper roasters cost more than air poppers and could probably get hotter than the $10 air popper I did, but I'd heard that generally people weren't getting better roasts out of those than if they had an air popper that worked. Drum roasters worked better, nearly everyone agreed, but cost, well, a lot more.
There's one odd machine in the middle, the Caffe Rosto. It's basically a fluid bed machine, but its roasting chamber is metal and heats up as well, giving it some of the properties of a drum roaster. (And it also does a roast at a speed about halfway between the poppers and the drums, giving the beans more time to develop. Some people say that's important.) It was, though, a little out of my comfortable price range.
Then, I came across a place selling refurbished units.
Mine came yesterday, and I decided to try one of the beans from the sampler pack that I had that called for "full city roast or darker." I put the roaster on full and discovered the difference between it and the air popper was dramatic. The beans got to a beautiful dark, shiny stage; nearly all of the chaff had been blown off, too. (The popper never did a good job of that, which may have been another sign of slight underroasting.) I'd be hard pressed to tell the difference between the Sulawesi beans I did last night and ones from a professional roaster. And the coffee this morning is great--although these aren't my favorite beans from the sample pack I've tried so far, I'd have to say.
The other thing I discovered about this roaster, which my roommates also discovered when they got home later, is that it's remarkably efficient at making the entire house smell like burnt coffee. (The coffee itself isn't burnt, mind you.) It set off the hall smoke alarm. This is wryly amusing because I never saw smoke from it--which I did from the popper, but the popper never managed to set off the alarm. Next time I'll either roast in the garage or make sure the vent from the Rosto is being blown right into the stove vent intake....