Hi! I read this and just wanted to mention, the keyboard/power button assembly is available on eBay for about $50, and it is in fact possible to do a swap -- I just did it. I wouldn't recommend it if you can find a way to avoid it, because it's a very laborious procedure and you have to peel off the two layers of keyboard illumination from the back of the keyboard, and then remove about 40 of the tiniest screws you've ever seen (which are spread across the back of the keyboard, connecting it to the topcase), but it is possible, and will save you about $250.
I have a feeling Apple doesn't sell the keyboard/power button assembly as a separate part from the topcase, which may give the impression that the procedure is not possible to do, however like I mentioned it's available on eBay. At first I was worried that the keyboard was permanently embedded inside the topcase like the white A1181 MacBook, but that is not the case, and after removing those 40 or so screws, it does come out.