Price for polishing depnds on the current condition of the floor and the desired results. This may mean one or sevceral grit levels. It may require resin bonded diamond discs or it may be done with Spinergy pads. Depends upon the floor.
I have seen prices from $1.25 per sq. ft. to $7 per sq. ft. For restoring heavy damage on neglected floor, you would be in the $5 to $7 range. For maintenance polishing on a floor that is being doen regularly and stays in decent shape, you would be at $2 or so.
Cleaning and sealing can also vary. Just like carpet cleaning there are high and low prices. I think the low end for cleaning might be 65 ro 75 cents a sq. ft for cleaning and an equal amount for sealing. But most folks don't want the cheapest deal for a valuable investment like a stone floor. Depending on number of sq. ft., expect to get $1.50 + or - to clean and about $1 more to seal.