Can just the shift solenoid be replaced in the transmission & at what fair cost?

Check engine light is on and the code says a transmission solenoid. In California if the check engine light is on it's an automatic fail for the smog test even if it has nothing to do with the emissions. The truck passed the emissions test but failed because of check engine light. Go figure. Any way I need to fix the tranny to pass the smog check and renew the registration.

There are no less that 8 solenoid specific codes on my generic DTC list. Best bet would be to go into your local servicing shop (recommend a transmission specialist) and have a proper diagnosis performed to determine the specific solenoid circuit that the computer is detecting fault with. Additionally if a solenoid is functioning properly and the commanded clutchpac is worn - it can generate a solenoid fault code. And in California, the check engine light is an instant failure. The computer detects faults that increase emission levels and so the computer generates a code.