The doctor's obligation is not to "find the cheapest possible treatment" (especially one where the over prescription of generic antibiotics is more problematic than beneficial), especially if the patient is informed.

In the individual case, it's dubious to suggest that surgery is a less conservative option than antibiotics. Yes, antibiotics are woefully over-used (though the overwhelming majority of their use — something on the order of 80% — is in livestock), but the physician's obligation to their patients is to treat their presenting problem, and in the way that is least harmful. Typically, that's taken to mean more conservative approaches first.