Firstly, my dad and I own and operate a non structural panelbeating and paint shop. As can be seen here: Auto Magic - Guaranteed dent and paint repair
Anyway, you guys make painting a front bumper sound like brain surgery. It's not. Even if it's metallic.
We would do a complete preperation - this means filling and priming the whole bumper which means that all imperfections, scratches and stone chips will be gone and then repainting it in the exact colour of the car for less than half the price the OP was quoted!
Usually the paint finish on cars leaving our shop looks better than the original paint from the factory as the paint is sanded again after leaving the paint shop and then polished. This means no orange peel effect at all.
We use Standox paints (as used by the BMW F1 team) and all colours are mixed from the computer to the exact factory spec.
Basically, if you take your car to any decent paint/panel shop, they should give you your car back better than new.
Forget about the dealer, take the car directly to the paint/panel shop.
Both the front and rear bumpers of my 156 were redone and they look better than new. If the GT is anything like the 156, the workshop might charge you a bit for labour for taking the bumper off seeing as the Italians saw it fit to use a gazillion screws to hold the bumper on. No really, I've never seen anything like it in all my experience in this field.
Anyways, hope you get it sorted to your satisfaction soon.