I think I would get a second opinion from an auto transmission specialist as it's a little too easy for Renault to pick the most expensive part off the shelf.
However my 3.0 24v - which I believe has a different box - had to have a new computer when a helpful professional steam cleaner filled the computer housing with water and wiped out the compter. Yes it was £700.00 and unfortunately it required a Renault only diagnostic computer to figure out the problem, so an auto trans specialist may just shake his head and send you back to Renault...