There are not many schools that even teach sign language, and if they do, most likely there is a fee.
There are many websites that provide lesson plans for free. At the Start American Sign Language website, each lesson plan is designed from beginner on to immerse the student both in the culture of being deaf and the use and grammar of finger spelling. It is also important to note that ASL is not an international language. If you want to learn international sign symbols, Start American Sign Language also provides that information. As a resource, the American Sign Language Dictionary by Martin L. Sternberg is considered the most concise and up to date authority. To find an online dictionary go to http://commtechlab.msu.edu/Sites/aslweb/browser.htm.
If you prefer to use educational videos go to http://www.aslpro.com/cgi-bin/aslpro/aslpro.cgi.
The best part of learning this way is that your can determine the pace. If you are having some difficulty assimilating the information, it is easy to retrace the lessons. As with learning any new language, there is the constant need for the two P's: patience and practice.
On some of the websites there are even games to help teach signing that foster fun and challenge. While perusing the ASL sites it is also very interesting to read up on all that is going on for the deaf culture.
For total access to information about signing, there is the resource website aslacess.org. OIC presents movies in ASL, so once you have become quite proficient check this out for free: http://www.oicmovies.com/.
On Youtube.com there is a very active deaf community so that people who sign can also access many videos, both music and ASL. The National Association of the Deaf provides free information about ASL. If you are a teacher, there is a website, http://www.needsoutreach.org/Pages/sl.html, that provides signs for different subjects, from biology to government.
To transcribe ASL into videos go to http://www.docstoc.com/docs/2547875/How-to-Transcribe-ASL-Videos-in-SignPuddle. For families that need support in dealing with the usage of ASL there is http://www.supportasl.com.