How much area are you talking about? A thousand acres? That is an expensive project if much less then that.

Depends completely on the method of weed control and the area to be covered. A custom applicator applying glyphosate should cost less than $15.00 per acre for an application, including the herbicide and adjuvants. If you have other weeds that require pricier, more powerful herbicides in spot treatments it would be higher, and if you are looking at strictly hand control over an area repeated several times, it could get pretty expensive on a per acre basis. After controlling the weeds, you can't just leave the ground bare as new weeds will quickly recolonize the area, so you must revegetate with something that will keep the weeds at bay.