Malware Bytes
Individually the cost of a single user is $25: https://store.malwarebytes.org/342/?scope=checkout&cart=29945
Alternatives to using Malwarebytes:
- MS Malicious Software Removal Tool: http://www.microsoft.com/security/malwareremove/default.mspx
- Spybot Search& Destroy: http://www.safer-networking.org/en/download/index.html
- Combofix: http://combofix.org/