I cant really offer any specific solutions to your question but, I have been conceptualizing this solution for about 5 years and I'm finally getting around to building my first robot. Anyway, making a couple of assumptions here that you need to communicate with the robot anywhere and up to 500M. WiFi is readily available but its too short range. RC control too short range and not reliable enough. The only wireless network with enough range that is available everywhere (for the most part) is cell phone. Cell phones with web browsers might be your solution. Verizon or AT&T now makes a phone that functions as a WiFi hot spot for up to 5 devices. So, you would use the cell phone network for your 500M anywhere range requirement and the phones WiFi capability to make the communication link to your robot. Most phones have GPS navigation ability so there might be some inbedded navigation solutions there.
(This is my first post on this forum and I'm really speculating here but in theory at least, its possible with off-the-shelf components.)
