It certainly is not free. Either the OEM who sold the device to you paid off Google for your access(i.e included in the hardware cost you paid the OEM) or you have to violate copyright(along with whoever uploaded them to the host who is vulnerable to a DMCA takedown) to get those apps.
Can you find me a legal link to some or any Google apps .apk file(s) to load on to, say the Kindle Fire?
Speaking as a purely practical matter, as an end-used you can easily get "gapps" builds for virtually any Android device though technically you will be violating copyright (unless you are using those "gapps" as a replacement for a 'backup' of the distribution that came with your phone originally).
After a botched cease-and-desist on Cyanongenmod back a few years ago (2009?) Google turns a blind eye to this sort of sharing of gapps. I've never heard of them taking any action against any gapps provider since that whole C&D debacle despite the fact that these files are shared openly all over the place.
In other words, these are definitely not free to the end user, the cost is just incorporated into the overall price of the phone.
I would disagree on the "reputable" part. Which reputable sites are they distributed on?
OEMs do not pay Google in exchange for bundling Google Apps.
>OEMs do not pay Google in exchange for bundling Google Apps
Do you have a reference to those two points? A lot of the small Android tablet OEMs have a lot of trouble getting Google apps.