ABC Rural has a good article about how UAVs in Australia are at the end of a 18 month trial to test the effectiveness. The UAVs fly in traditional aerial survey patterns, capture imagery down to 1cm pixels, flight levels of just under 400ft, and within line of sight.
The article mentions flight costs of $30-50/hr and consultant doing the flights, not the farmers or larger agriculture interests. The ROI is planned around small, 80 hectacres of imagery.
Unless flight rules change through CASA (FAA of Australia), flights will continue to be through contractors who have gone through the approval process, which is long and costly and not cost effective for the average farmer or larger agriculture interest. CASA will also need to change the flight rules to allow flights outside line of sight to be useful for larger agricultural plots.