Can’t speak for mechanical keyboards specifically, but finding what you want for the cheapest price is most often done best on eBay rather than Amazon.

I’ve also used VoIP.ms. Making and receiving calls is possible but requires setting up a SIP client app on your phone. Getting the settings right can be tricky.

Look into fixed wireless or 4G/5G home internet. Fixed wireless is sometimes exactly what you need in spots like that. It is not 4G or 5G, sometimes it is just long range WiFi or other lax spectrum.