www.Dona.org -- on the left hand side of the page you'll see a little purple bubble like area that says, "Find a doula!" - just fill in the bubble for 'birth doula' and click your state. Voila! Doula recommends!
You can also look up doula TRAINING classes in the area, then call them and ask for the names of their recent graduates. Many of them doula for free.
OR look on craig's list. I'm a doula and often post ads on craig's list (I'm not affiliated with DONA, even though I was trained by them - I just don't take on enough clients, and I don't charge them enough, to warrent paying fees every year - plus I advocate unassisted birth, which is something DONA and a disagree on).
HTHs!