If it sounds too good to be true, it probably is.
How do you know the Audi isn't suffering from something similar to what the LS's suffer, like failing coils, or lord knows what else?
Maintenance is expensive on German cars, this is true. It costs 120 bucks just for an oil chance on some cars I own. Now, granted, the oil change is good for 10,000 miles (which I don't trust, I do them every 5,000 miles). But parts, labor, and general maintenance is a lot more than on say, an LS.
Keep that in mind. Don't buy (trade in your case) for a car you can't afford maintenance on.
And for the record, I'm not implying you couldn't afford the maintenance on it. But if you don't have a factory warranty, you should have at least $3,000 stashed away just for when stuff breaks down on that audi. It may not cost 3 grand every time, but with their reliability (or lack thereof), you might end up shelling more cash than you'd want.