Some dentists take Medicaid, some work on a sliding scale, some will let you make small monthly payments to pay the bill. And you might want to find out if there is a dental college near you. Dental colleges will do dental work at very inexpensive rates. Incidenitly, some therapists and psychiatrists will work on a sliding scale too.
It may take a little effort to find these people but this is why God, Al Franken, and Al Gore invented the internet.