My two cents.
Charge by the hour unless you are VERY confident in your ability to quote and to estimate the size of property. Nothing like giving a per-acre price and then finding a bunch of obstacles that mean you have to go slower than you thought.
Never take a customer's word on the size of a property. If possible, confirm the size using Google Earth before going out to mow.
Depending on the size of the job and the distance to travel, you may want to waive a travel fee. If the job is close and large-ish, it may make sense just to roll it into your overall profit for the job. Don't forget that your time hitching up the trailer, loading the tractor, traveling to the site, and so forth, are all work-time that you are going to have to get paid for one way or another.
Calculating overhead. Start with the fuel cost of your tractor per hour. Now take the cost of a 400-hour service and divide it by 400--that's the beginning of your maintenance overhead. How much will a major repair on the tractor cost? $1000? Okay. How many hours are you going to run before you hit a work-related major repair? Divide that out and add that in. Continue this line of thought forward.
Do you have liability insurance? You do have liability insurance, right? Well, if you don't, that's up to you, but if you do, take your annual premium and divide by the number of hours you work in a year. That's your overhead for insurance.
Etc...
tl'dr: Go look on Craigslist for bush-hogging advertisements and see what they're charging. When you say "north texas," I guess you mean DFW instead of, like, Lubbock or Amarillo, so I checked Dallas CL. Looks like about $45-50 an hour, although lots of people don't advertise their rates. If you're really motivated, just call one of them up and pretend to be a potential customer to get a quote.
dallas all services classifieds "bush hog" - craigslist