I hope for your sake it truly is a non-load bearing wall! That being said this job would probably cost anywhere from $1000.00 to $5,000 depending on how bad the damage is and what the cause of the damage is. I am not a licensed contractor, this is simply based on my 18 years of experience as a real estate agent.
Your best bet would be to have 3 licensed contractors look at the job and give you quotes. Good luck!
Mitchell S. Feldman
Associate Broker/ Director of Sales
Madison Estates & Properties, Inc.
Office: (718) 645-1665/ Cell: (917) 805-0783