Audis are fine so long as they're under warranty. It seems that once they cross that barrier, is when things go to shit and the TCO goes through the roof. I'm a big fan of the Beem Dream too, but they're also expensive machines to maintain.
The insurance for an LGT should be cheaper. Mine wasn't significantly different than what I was paying for my 09 STi (similar coverage, except I have a full glass coverage policy on the Legacy.)
At this point in time, all the DECENT 05 LGTs seem to be running in the 10-12k range, depending on trim. If you're finding one at 7k, look very closely to make sure there's no issues. (That, or you found a killer deal...)
The Spec.Bs are more expensive and definitely account for a chunk of that price fluctuation... but consider that you're looking at a car that spanned 5 (almost 6) years of production. Price variation is normal.