I've hired quite a few in the Marcellus and Utica and $250 per hour is probably the average. Obviously the total price depends on how much contact the attorney has between you and the lessor and the amount of time preparing revisions and/or addendums to the lease.
When I was investigating several years ago, it was like either 1/3 of what you got or some percentage of the royalties. I signed with a landowners group in the end, so that didn't matter.
Giving an attorney a percentage of the bonus offer is not a good idea. I would say an Attorney should be able do everything your asking about for $1,000 or less. You could be handing them tens of thousands of dollars for no reason.
Hahahaha. Yeah! Seriously!
I would say that it depends on how much they are doing for you; a simple lease review may be a couple of hours at $250/ hour, but if they are doing the negotiating or other services, such as clearing title and old claims, it will go up quickly from there.
I know some local attorneys here in Ohio who charge $100/ acre and handle the negotiations. If you have a complex situation, 10% to 15% of the bonus can be reasonable; I can't see a situation where any higher is reasonable UNLESS they have to handle litigation for you.
My lawyer had to clear an old lease through forfeiture, fight the old company, clear title, and negotiate a new lease, and is charging 10% of the bonus payment.
As a CPA, I believe professionals should be charging you for value delivered and you should be willing to pay for that value. Generally that can be tied to an hourly rate. My guess attorney fees would range from $200 to $500 per hour. Unless the attorney is negotiating a higher per acre bonus or Royalty percentage, I don't quite understand the per acre charge, other than they are happy to share in your wealth.
If your oil & gas professional comes up with a solid or profound idea that positions you favorably, you should be willing to compensate them for those benefits.
In the end you need to determine whether your professional is providing the appropriate value for the price they are quoting. There are many good attorneys, CPAs and investment managers out there that actually earn their fees through their own efforts not your good fortune. If you put together the right team of professionals you can bounce these issues off the others to hopefully get to a good spot.