Chevrolet Repair: odometer/speedomoter not working, diagnostic fee, proper knowledge

Question
what is wrong with the car if the odomoter and the speedomoter don't work and how much should it cost to fix?

Answer
What year is the car?
What is the make, model, etc.
If it is an older model car, there is a plastice wheel in the transmission that wears out.
It doesnt cost that much to replace yourself.
Shops, depending on where you live, the type of shop and how busy they are, should charge around fifty dollars at the most, unless they charge a diagnostic fee.
But without the proper knowledge of the vehicle, dont hold me to that!