A firewall can actually be less expensive for an organization in that all or most modified software and additional security software could be located on the firewall systems as opposed to being distributed on many hosts. In particular, one-time password systems and other add-on authentication software could be located at the firewall as opposed to each system that needed to be accessed from the Internet.
Other solutions to network security such as Kerberos [NIST94c] involve modifications at each host system. While Kerberos and other techniques should be considered for their advantages and may be more appropriate than firewalls in certain situations, firewalls tend to be simpler to implement in that only the firewall need run specialized software.