1-The input shaft speed sensor tells the transmission how fast the car is going so it will know when to shift , so if it is not working it will cause the flashing light
so it need to tested & replaced if bad before you change the transmission assembly
I have sent a diagram showing the location of the sensor for your review
2- The sensor is : $143.45 , the sensor is located on the outside of the transmission assembly ,so replacing it only takes 0.8 hrs , so around $75
and diagnostic time an hr , so you look around $200 $300 ,depending on where you take it to get it done .
3- I would definitely suggest another opinion , and dont change the transmission unless you confirm that the sensor is good and working
and the problem is internal and not the sensor before trans replacement
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