Not a laguna, but i have fitted one to my trafic van.
Interfaced into the sat nav screen, switchs over automaticly when reverse selected.
Interface was about £140 from germany, Camera £40 from
. took about 3 hours to fit, all wires hidden, camera fitted in the read door etc. It's very cool, but not sure if you really need one on a laguna.
Your choice I guess.