I have in the past been pleasantly surprised at how reasonable main dealer prices were for such parts.
In any event, it may be best/easiest to get them to confirm the size of your fitted wheels.
Depends on if you want a match with your other wheels, or just a keep-you-running wheel I guess?
If not, then if you take a wheel off, you will often find the size and offsets etc cast into the rear, inside face of your wheels.
In the past I have used this info to go to a scrappy and buy used. I wouldn't be surprised to find that the mk2 wheels are the same as mk1?
I don't have my car with me atm, but I seem to recall my SE has a steel space saver, and there is not a lot of spare room in the wheel well.