Any garage worth their weight will check for causes for you too.. cos may even just be down to something simple of over full of oil.. but obviously could be completely the other way and something major...
As Butch says... nothing will be known for sure till the job has been started.
I cant comment on pricing as i dont know what its like over your side of the pond.. But any job on most cars that includes dropping the transition can be a timely one unless front wheel drive, then can be shortish some times