If you buy all the necessary conversion parts brand new from a dealership, it would be about $1500 (one 3rd gen 4Runner owner did that a few years ago). The ORS kit cuts costs and uses less expensive aftermarket parts to get the price down to about $1000. There are lots of parts replaced, including different half-shafts. It's not at all a simple install especially due to the wheel bearings.

Jeff
2000 4Runner SR5, supercharger, rear e-locker, ARB front locker, 285/75R16 MT/R's, custom bumpers & skids
2007 Tacoma double cab 4x4 - stock