I must confess to lurking on these boards for some months now, have to say they have been very informative.
I have had my Alfa Brera for some time now and I'm having a nightmare with phone card sim tray, it snapped and my Alfa dealer have said they cant get the part, the only alternative is to purchase a whole new unit at a cost £1800
I didn't even know there was an option for a SIM card tray on the Brera!!
All I can suggest you do is get the part number and ring round a few other dealers. Also try independants such as AlfaShop and EB Spares - if you have the part number they maybe able to get you a better price. Membership of the Owners Club can get 10% off spares at certain dealers so that's a help too. You could try ringing Alfa UK direct and telling them what you think!
Other than that all I can think of is to get a Bluetooth kit fitted and ignore the tray.