Realizing this is not about securing a standard tourist visa for a vacation, but rather for those navigating complex immigration proceedings or appeals. Just letting you know that the Executive Office for Immigration Review (EOIR) provides an official list of pro bono legal service providers.
While many assume expensive counsel is the only path, this list outlines recognized organizations and accredited representatives available by state. This ultimately will be the most reliable source for low-cost aid.
The CONSTRAINT requires attention: these providers are generally for individuals already IN the United States facing immigration court proceedings. Make sure to verify the specific restrictions for each provider, as some limit their services to specific sub-groups (e.g., asylum seekers, detained individuals).
So FYI, observe the detail in the state-by-state breakdown before committing to paid services. History lives here, in the details of the law.