Seems like they could just break up the top layer of soil with a bobcat instead of spreading so many chemicals in your yard??
NOT a good idea..
You'll kill the grass, and realease additional dormant weed seeds.. (learned that lesson the hard way)...
If your land is fairly flat, and you don't need to plow/till don't..
Kill off the grass and weeds and reseed..
Thinkin $1400 is a little steep, but if it were me I'd hit it with Round-Up twice.. Hit it once, let everything die off, then 2 or 3 weeks later hit it again. Round up in a 40 gallon sprayer should be enough for an acre.
Rent a seed drill and reseed..
(Carroll's has one, but you have to rent a tractor too)