Before you do anything else go look at the property. You need to see and measure what they want you taking care of. If you bid on 200 acres and in reality there are 2 acres of grass and 198 wooded area. THink you will get it?
If you have 3 60" mowers it will take you around 15 hours to mow it. That's assuming 8 mph. You going to trim and blow? Spot treat for weeds? Prune? Mulch?
get some more info and figure your time to do the job.