I dont know the list prices of A7, or the differing specs, but if it is the car you want have a look at pre reg cars as well. I had a quick look and this one jumps out:
Presumably a big saving on list, 100 miles on the clock and probably more to discount. I would be inclined to look at something like this with an even bigger saving off new and not budge until they give you a decent APR, or look at financing with another company.
EDIT, sorry it was the BiTDi, there is this one