Welcome to TBN.
You didn't say where you were, which may or may not help with this. I'm not the type of contractor that you are looking for, but I have hired contractors for various projects and can offer a few things that you can look for.
First, ask around to see if there is somebody that others will recomend. A little footwork on your part may save you thousands of dollars and avoid allot of frustration. Word of mouth is always the very best way to find those who do good work and leave their clients so happy with them that they will recomened him to others.
I always tell others and try to do this myself, talk to at least five people before hiring anybody. What usually happens is the first person you talk to sounds great and you decide to go for it right then and there. Make it a point to talk to five and not hire anybody until you have talked to all five. More is better, but there is a point that you are wasting your time to. It's up to you to decide when that is.
Put everything in writing. While there are plenty of honest, hard working heavy equipment operators, there are also allot of thieves out there. Some will work hourly, others will bid the entire job. Either way, there are ways to take advantage of you. I like hourly if I can keep an eye on them and make sure it's agreed that I'm paying for hours that the equipment is worked. Don't let them try to do repairs or maintenance on the clock. Coffee before starting is on their time, not yours. Write down what time the engine starts and when they shut it down. Too often I've seen them guessing at when they got started and about how many hours they worked that day. Keep notes and let them know you are keeping notes. Nothing like a document to keep everyone honest.
If you get it bid on for the total job, be specific of what you want done and how you want it done. Be sure to include deadlines. Don't assume that they will clean up after themselves, or even make it look pretty. That needs to be in the contract.
Whatever you do, make sure that you don't pay upfront money and that you don't pay them off until the job is done. Hold back enough to keep them honest and hungry to do it right. Some people are pros at sob stories. It's their problem and you should never listen to their stories. It may be true, but usually it's just a story that they are very good at telling. Don't give out any money until it's due. I like to pay after a pre arranged part of the job is completed. It might be as small as getting the equpment on site, to as big as the last ton of gravel being graded out. Just be sure to have it in writing before anything starts.
Price will depend on how big a machine is used and how many machines are used. More horse power means more money, but it also means the job will be done faster. I would always hire as much power as possible. While a small machine can get the job done, a bigger one can do it three to four times faster. Sometimes more. If you can pay twice as much per hour for a bigger machine and get the work done three times faster, the bigger machine is going to be cheaper.
If you cannot find anybody by word of mouth, then be sure to ask for and to check refrences. I have pages of refrences that I have available for clients. I haven't given any out in years, but I still have them for those who might ask. It's also my contact list that I keep so, eveyone that hires me is on my list, and that's the list I give out if asked for. If they don't have refrences, run away. It doesn't matter how cheap they say they are, it's not worth it. There are a dozen ways to be taken advantage of, and those who are dishonest will do it without a second thought. Some are just evil and think it's their right, others are clueless and will never realize the pain the cause others by their disorganization, incompentence and laziness.
Good luck and keep asking questions.
Eddie