The single biggest cost driver is how far the mold spread and whether it reached hidden areas. A patch on bathroom drywall is a contained, low-cost job; the same mold that traveled into wall cavities, the HVAC system, or a crawl space multiplies both the labor and the containment required.
Material type matters too. Non-porous surfaces can often be cleaned, but porous materials like drywall, carpet, and insulation usually have to be removed and replaced, which is where cost climbs. A proper remediation also fixes the moisture source, without which the mold simply returns and you pay twice.
Most reputable Kansas City remediators, including Heartland, provide a free on-site assessment and a written scope before any work, so you see the range for your specific situation instead of a guess.