The cost to level a concrete floor will depend on how much out of level the concrete floor is.
The process of leveling a concrete floor is known as mudjacking and leveling the concrete floor can cost anywhere from $500.00 to $1,500.00 depending on how much it's out of level and the size of the concrete needing leveled.
Sometimes the cost to level the concrete floor can be as high as $2,500.00
So it's best to get several estimates from different companies before having them perform the job.
However don't just base the decision on price alone also base the decision on how well the company does the job.