I need the unit cost to be no more than $100 USD. Ideally positioning and communication will be less than $70. Security and latencey are not a big concers at this point. ATM all I know that absolutely need to be sent are latitude and longitude and maybe some sort of identifier code since more than one unit may be communicating with the base PC. I was thinking of GPS and Dirt Cheap Dumb Wireless but cannot find anything about the approximate range using DCDW.