Not all Open Access Journals require an article processing charge (APC) to publish your work. In fact, research has shown that less than 50% of all OA journals have charges associated with publication.
Before assuming that you need funding for an open access journal, check their Information for Authors page or their website to see whether there are any costs associated with publication.
Iowa State University provides a variety of grants and discounts for faculty, staff, and grad students who are in need of funding for their publications.
You can cover publishing charges with outside grant funding as well; however, funding availability will depend on your discipline and your need.