Depending on what weeds and at which stage you want to kill it can be 1.5 quarts to 3 or more quarts per acre. It normally runs me about $12 dollars per acre to spray my own not counting my labor.
Just had my pasture sprayed by helicopter for $32 an acre. Southland Spray Services did it. They work in Texas, Louisiana, and Arkansas. It took them about an hour to spray 100 acres. That's alot quicker than I could ever think about doing it.
I'm to big of a tightwad to pay 32 dollars an acre. I could do it myself and save $2000. Heck for that much money I'd even park the spray rig and do it with a 4 wheeler to save that much money. I'd take that $2000 and turn it into $2500 in a years time. But then again I am tightwad but I do make money on my cattle.