A bathroom fan replacement and mold remediation solve different problems. A fan can support moisture removal, but it does not establish the source, extent, or treatment requirements of visible mold.
Replacement cost depends on the fan, controls, opening, duct path, access, electrical conditions, and agreed scope. Remediation cost depends on separate assessment findings and should not be predicted from a ventilation symptom alone.
If a bathroom stays wet, start by documenting the fan operation, condensation, visible finishes, room use, and any known leaks. A ventilation review may identify useful next steps without promising that one improvement resolves every contributing condition.
Seek appropriate qualified help when there is extensive visible growth, suspected hidden damage, an active leak, unsafe access, or a health concern. Bathroom Fan Pros does not present fan replacement as mold remediation.