FAA requires 18 months of practical experience with the equipment and materials used in maintaing and altering airframes or powerplants (18 months per rating); or 30 months of concurrent pratical experience performing actual maintenance and alterations of airframes and powerplants (for both ratings).
Schooling can cost you anywhere from a couple of thousand dollars to more than twenty thousand dollars for the required 1900 hrs of instruction for combined A&P ratings. It's worth looking at the FARs to see if any of your experience will qualify as practical experience and trying to test out of those areas.
Your local FSDO (Flight Standards District Office) should be able to help you with more detailed information and local resources.