15' Batwing hourly rates

I'm in the process of rebidding all my contracts for field mowing 2016. I don't have a lot of fellow farmers who also bush hog to compare rates with. There's no "field mowing" forum, so this was the one I picked to ask the question:

 

What do you charge per hour to run a 15' batwing over fields?

I'm not talking heavy brush here where you go slow-just fields resembling overgrown hayfields. 

I currently shoot for $85/HR under 25-30 acres. Higher acreage would be a lower hourly rate(quantity discount), but honestly, I usually dont do more than 30 acres at once anyway. If its heavy brush & saplings, I charge by the job. 

 

15' Batwing hourly rates