Is $2,500 to level the subfloor and lay new plywood a fair price?

I contracted Home Depot for wood floor installation. They informed me that additional costs might arise during the job if subfloor preparation was required. After they tore out the old floor, they asked if I wanted them to proceed with additional work to level the floor and lay new plywood for an extra cost, which I agreed to. I am now unhappy with the level of the floor, especially near the door, despite paying extra for this service. I also noticed some defective boards that I had to fill myself, and the spacing isn't perfect, with the subfloor visible in some places. I wish they had been more upfront about the potential need for leveling before starting the job. I've had other issues with Home Depot on previous jobs, including a countertop installation, and a manager had promised to make up for the counter issues, but that manager relocated. I haven't pursued action on the floor yet because the installers were good young men, and I don't want to cause problems.