So after doing lots o research on the web and phone....The cheapest I found the sensor to be was 123.99 which was also the dealer's price for the sensor so I let them do it...
The cost break down:
$117.99 to look and diagnose at the ABS system
$123.99 for the sensor itself
$107.99 Labour to install (this is BMW standard daily rate-which isn't so bad)
$37.99 State Inspection passed!