My speedometer is going crazy, what's the cost of repair? I leave in Illinois.

What is your question?

Just bought this vehicle Dec 28th with 53k miles on it. Riding around town has been great - no problem. However, today I went onto the interstate and my speedometer said I was going in excess of 120mph and my Tom Tom indicated 62mph (think the tomtom was correct since other cars were passing me and the cops did not pull me over). what is the cost to repair this?