Some thoughts:
1. The rule of thumb is that a rebuilt title is worth about 50%, maybe 60% of a car in similar apparent condition, with a clear title. If $42 is retail for this car, then $21K would be reasonable.
2. Forget goodwill, dealership help, recalls etc. on rebuilt cars. You are on your own.
3. Titling, registering, insuring all are an increased hassle on rebuilt cars. In many states, many insurers won't touch them.
4. Any rebuilt car will always have a safety question mark. To become a rebuilt title, somebody had to make the call that that getting the car back to pre-loss condition was economically infeasible. Then somebody had to decide to do it cheaper. Maybe that happened correctly, maybe not.