[Binny]

Sorry to hear about your problems.
To see the cost of that quote makes me thankful I shelled out for the extra MyFord factory warranty to 200k.
If you do have to get the sensor changed I assume it must be inside the transmission based on that cost. If it has one on each gear shaft it might be worth asking how much to get the other one done at the same time. Most of that cost is probably labour to pull the transmission out and pull it apart.
Hopefully you can get it sorted for cheaper.