The only way my air or heat work is in the High position. Being it’s an older car is it worth repairing.
Chances are it is the blower motor resistor. The part is generally less than $30, But part price and labor will vary depending on your location. There might be a YouTube video for your specific car showing how to do it yourself.
If your vehicle looks OK and starts , stops and drives decent even if repairing the fan costs 200.00 ( Guessing ) where are you going to find something for that price.