New Member with a big question
These cars popped head gaskets all the time. My first 318 did within the first 100 miles of me owning it, and it was my first car project in my life. In terms of pricing, you need to know if it just overheated, or warped something. How long was it driven with water in the oil? What does the oil look like? The estimate of $800-1000 is accurate. but really, they should tell you it's an hour or two of labor to determine how bad it is, and then they get back to you.
That transmission estimate is BS. A full race trans will cost $2500. A rebuilt torqflite, either 904 or 727, is under $1000 from the shops in CT, which typically are pricey. Figure at most $1200 with a new convertor and aux trans cooler if needed. I would have the engine diagnosed, then see what you want to do. Shouldnt be more than $200 to have that done.