After quite a bit of lurking over auctions, I managed to get a Sega CD (model 2) for $35 (plus $15) shipping. Also included are a Genesis model 1 (which I already have, so trade-in fodder), the base extender so the model 1 Genesis fits on the thing properly, the metal plates, etc (all of which can go for a bit just on their own)
... Not included, unfortunately, are any of the cables. Since I already have a Genesis 1 and 32X and such, all I really need is an aux cable to get the audio mix going (easy enough) and another MK-1602... which might be more of a problem. I do have one of those generic Retrobit "universal" AC adapters for NES/Genesis/SNES (came with my toploader NES), but I've heard they don't actually work so well with Genesis..es and barely at all with Sega CDs (not surprising since it only outputs 850 mAh instead of 1.2 Amp)
Still, I feel like I did pretty well