@Massimo Dutti is sort of the middle ground, you get good quality and the price makes sense or @ZARA Men has great fitted shirts for about 40 JDs, @Cortefiel & @7 Camicie have great shirts but are more expensive, around 90.
@Auto Mall has a few places with specialized number plates, but if you're just looking for the normal ones, you need to go to The Drivers and Vehicles Licensing Department in Marka or Salt.