A lot of insurances do cover addiction rehab, so definitely check with your carrier if you have insurance. Support groups and 12 step programs can be really great free options, and people you meet through them may also be able to offer suggestions about affordable treatment. There are also federally and state funded treatment centers that are usually more affordable than private rehab, although some private rehab centers set aside funds for charity cases or will help you set up a payment plan--it never hurts to ask.
You can also start by visiting a community health center to meet with a social worker or psychologist--they often operate on a sliding fee scale, so you only pay what you can afford. The visits may be helpful in treating your addiction, and many mental health professionals will help you find a way to afford treatment. These websites can help you find one:
Click Here to search for a treatment center in your state that is right for you.