Hello and thank you for trusting Just Answer with your question. I'm Dj and I will work with you on this.
I believe the part you are talking about is the transmission tail housing. Here is a picture.
If that's the part, I would expect the cost with labor to be just short of a thousand dollars.
This is going to be difficult to find used, which means you will have to get it at a dealership. Labor should be around $200-$300.
If this isn't the part you are talking about, let me know and we'll go from there.