Several people on the web have blog posts on their experience of getting a green card without a lawyer, here are some of them:

gypsytracks - on getting a U.S. green card

Haining Zhong - Green Card Application Without a Lawyer

Associated Content - Getting a Green Card Through Marriage - What to Expect

As you can see it is possible to apply for a green card through marriage without a lawyer. However, to save you the time and effort of learning all the legal jargon and filling the forms, Easygration Gold or Platinum packages offer a great money and time saving.