For under $17k, there is nothing even come close to the Audi A8 D3, which started in 2004 and ended in 2010. It's a joy to drive and every luxurious feature included. It's an A8L, so it's long and the back leg room is abundance. Most of these are kept well by the owners, but some aren't, so we really have to look for the right car with the right owner.
In 2004, most of the A8 come with almost all options that one would need to be comfortable to drive the car and most of the A8 are A8L.
Cheers,
Louis