You could try Zigbee. It has range up to 10km. It also appears to run in the licence-free band in many countries.
XBee and ZigBee for long distance signal transmission
https://ham.stackexchange.com/questions/3729/do-you-need-a-radio-licence-to-use-zigbee-xbee
If you need to go further later, I'd suggest you setup repeater units.