Depending on the land condition, with GMO seeds you can skip a spray. You save money on the herbicide + time/personnel + equipment + diesel.
Here is the breakdown for soybeans. Note these numbers DO NOT include time/personnel, equipment costs, or fuel. This is only herbicide costs:
Non-GMO (double spray) = $41-$77/acre
Roundup-Ready (single spray) = $43-$59/acre
Roundup-Ready (double spray) = $55-$75/acre
Liberty Link (single spray) = $42-$50/acre
Liberty Link (double spray) = $54-$66/acre
With good land management practices, most farmers can easily avoid having to apply the second spray. This is a HUGE cost saving and most farmers are aiming for that. I can tell you from personal experience, avoiding the 2nd spraying is the difference between successful use of GMO seed and barely breaking even with a crop.