I am often asked "How much would I make as a public interest lawyer?" There are many types of public interest law (see my blog posting from February 2009); accordingly, there is a wide range of salaries, depending on the type of work, employer, and location.
Most federal agencies use the "General Schedule," or GS Pay Scale, which has "grades" and "steps" to cover salary ranges. Happily, there are significant cost-of-living increases for some metropolitan areas. Federal banking regulator positions, with agencies including the Securities and Exchange Commission, pay on a higher scale. Raises allow many federal attorneys to earn six figures within three years of their start dates.
Entry level salaries for positions with state government (including assistant district attorney and assistant attorney general jobs), public defender offices, and non-profit organizations vary considerably, from $34,000 to over $90,000. For more information, see the research about public sector salaries compiled by NALP, the Association for Legal Career Professionals.