Depending upon your financial means and your goals in SAR this could be a lot of money. If your interests lie in lost-person search exclusively in urban or suburban areas, then your training may be at no cost and/or your expenses may be minimal. Expenses for anyone interested in being fully prepared for wilderness search may invest over $1,000 in the process easily. For wilderness searchers the expenses break out into at least three cost categories:

Equipment - It may cost a lot to fully fit yourself with an appropriate pack, clothing, boots, GPS receiver, amateur ("ham") radio, and other gear if you don't already have suitable back-country gear and clothing.  Other costs such as a trailer for search and rescue continue to come out of the volunteers pockets because there is just not enough funding in most states.
Training/certifications - Quality instruction may run additional if you pay tuition + travel costs to a basic wilderness SAR course or a wilderness first aid course. Certification fees for the NASAR's SARTECH skill/knowledge evaluations will be at least $70. The FCC amateur ("ham") license test costs money.
Recurrent expenses - Recurrent costs include transportation and other expenses at searches and training, and replacement of "consumables" such as batteries and snacks in your "ready pack.  Many members keep MRE's on hand for searches which can be costly.