from the perforcelicence page:
Free Licensing for Open Source Development
Organizations developing software that is licensed or otherwise distributed exclusively under an Open Source license may be eligible to obtain Perforce licenses gratis. This includes upgrades but not support. Perforce Software reserves the right to approve the Open Source license; those fitting The Open Source Definition, including the GNU and FreeBSD licenses, are good candidates. Execution of a End User License Agreement for Open Source Software Development* is required. Contact us for more information.
for open acs it looks free
