Investigate community based schooling options in your area. Depending upon where you live and the demand for various jobs in your community, sometimes local and city governments will pay for certain types of schooling required to fill job vacancies. If there is a shortage of truck drivers locally where you live this can be a very realistic possibility.
Take the time to speak with your present employer about paying for your schooling. If you currently have a job where you drive for a living but don't have a commercial driver's license, many times your employer will pay for your additional schooling. With an upgraded license you'll be more valuable to the company, and if you've been a good employee they won't mind making a small investment in you.
Participate in a work study program. Some driving schools offer free tuition if you agree to work for them for a specified amount of time following the completion of your training. This can prove to be very beneficial because you can get your education and real world experience all at once.
Apply for a job with a company that is willing to train new drivers. On the job training is a great way to get your commercial drivers license schooling paid for, and many companies desperate for drivers are willing to train newly hired employees.
Contact individual truck driving schools to see if they have need based funds available. Some truck driving schools have tuition subsidies available for financially needy students. If you qualify for these funds you may be able to attend classes free of charge, provided that you remain in good academic standing.