The best way to attend CNA classes for free, is to do on-the-job training. Many hospitals and Nursing home facilities offer free CNA classes, some require you to work for them for a specified amount of time. Some places have an earn while you learn program. You will need to contact the places directly for more information about the requirements.
You can also get free CNA certification classes through different programs in your state if you qualify, such as the Displaced Homemakers Program, The Workforce Investment act (wia) and through the Job Corps.