Need help on help desk system

I need help finding a help desk system for a startup company. Obviously, they can???t afford a $5000 solution and they have minimal support staff. I was hoping to find something free or low priced that I can show them. The help desk should have ticketing and a history for each ticket + the ability to map to departments (support, sales, etc.) for future growth. Is anyone using a system that has this and is free/cheap?