tranny speed sensor

anyone know how difficult it is to replace the transmission speed sensor on a 98 4.0 auto? The idiot light came on for check engine and i was told this is the culprit according to the codes. Also, anyone know a good place to order one cheap? Thanx for the input.

The sensor is on the rr housing just ahead of the t case. ATF will come out when you pull it so have the new one ready to thread back in right away to minimize the mess. Very easy job. Left side of the trans.