If it's rusty, it's probably long past due ready for replacement. I've never seen one rust.
Got to agree with Kelli. They should be stainless steel.
You might have to replace it.
I agree with the others. I've had a disposal ever since I had my own kitchen. I've never seen one rust. Have you tried cleaning it with lemons? It might just be dirty????? Cut a lemon in 8 ths, put the pieces in the disposal, turn on the water, then the unit. Run until lemons are gone. Turn off the unit then the water. I hope that helps. Wishing you the best.
Yes I agree it is time to replace it. They are not that expensive.