They probably got them for next to nothing anyway, and they've been breaking them for parts and the box (where do you think they get them for the refurbs?). Chances are they've already made the money back a couple of times over. For comparison, a new in box PAL Taiwan Megadrive II (a really rare model, Japanese case but european internals) goes for £20 plus shipping. I'm not too much of a fan of amigakit's buisness model.
Their business model is the same as any others. Buy low, sell high. Any business that doesn't follow this basic principle doesn't stay in business for very long.
For example Apple's costs for making the iPad are somewhere around $230 according to CNET, and they're selling them for $499.
