I can only speak to my experience in Florida. Your state may vary...
I had two options for legal representation:
1. Pay a flat fee based on the estimated size of the estate and the complexity, i.e. is there a clear will, is it INTESTATE (no will), etc...
2. Pay a percentage of the estate value at final disposition. This precentage was dictated by the state based on a schedule. XX% up to $1.2 million, xx% added to that base number for more than $1.2M but less than $XX, etc... the numbers are made up, but you get the idea.
In my situation, I opted for the percentage, as the initial estimates were lower, I believe this was a mistake. I personally would take the flat fee if I had to do it over. It seemed initially like it was excessive, but would probably have saved us $$ in the end. The reason I say this is that it is my belief that the lawyer manipulated the values of the estate in his favor...things like land valuation, personal property estimates, and so on.
My advice; Hire your own appraisor for the personal property, hire your own property appraisor, and hire any one else that has to provide estimates of value yourself. Do not let the lawyer handle those things.
Hire an estate lawyer as near to you, within your state, as possible. Do not hire any old P.A. as they don't know the ins and outs of estate law, and will cost you time and $$.
Remember, my advice is free, you usually get what you pay for. Good luck.