Home of the original bird, where I can get a "bird" with a stick for about $7, and replacements for about 3/$9, I think.. they also have a few other replacement attachments that my cats went nuts for too, particularly the mylar attachment.
Definitely order refills. Don't leave it out anywhere they can get ahold of it, aside from the string danger, they will mutilate the bird and there is no where you can put it that they won't figure out a way to get to. I have to put mine behind a locked door.
They're not sprayed as close as my nose can tell, and my cats have no real interest in catnip toys anyway.. although they do like regular catnip.. but they love feathers, and they love the chase. Da bird flips and rotates and makes noise, and all of mine love it.
If you're paying $12 off of ebay, though, you're paying too much. The one listed on ebay is the exact same things offered on go-cat, which is the original maker of da bird.. and I think it's a bit cheaper on their website, although not sure about shipping.
From go-cat: 5.95 for da bird w/ stick
da bird refills 3.50/one $10/3
and the three others they show there are $2, $2, and $2.50... shipping to my address ends up being about the same, I think.
Anyway, you can get things cheaper if you buy more of them, I think. Either way, I've found that they're cheapest when purchased from the go-cat site (barring ebay, the wonderful world of deals)...in stores the price is really marked up.