You are quite correct a genuine Apple keyboard is around US$400 and also as I said, the install is complicated, but not impossible. Definitely a tech job. Be aware of course, that these keyboards are mass produced for Apple in China, same source as the after-market keyboards. The longevity of the keyboards are no different, in my opinion. Particularly as the Apple installed boards have constantly been given to failing. Way past warranty of course, so what the hey? It's a matter of personal choice. There were some excellent fixes that anyone could do to replace the faulty keys and even some removed and cleaned with alcohol and replaced. These are shown in easy steps on YouTube. Sadly I was too late in replacing keys and of course there was no guarantee that they were the actual cause of the failure. I will however have a go when I have the time and now that I have the necessary tools. Not urgent.
If you do decide to look for steps and perhaps keyboards (new) on eBay be specific in your search i.e. 17" MacBook Pro Keyboard and year of model plus model name if possible (should be on the back of the case).
My next search will be for a tech prepared to install at my risk and at a realistic price somewhere on the Sunshine Coast, Qld. If anyone knows of one, please let me know.