If you buy a 06 A6 or newer, they are pretty reliable IMO. As a ex-Lexus owner, I can tell you that the Lexus parts and labor cost just as much as the Audi.

speaking from experience maintenance on an audi is not what your going to expect, spark plugs and oil change are not to bad and can be handled by most diyers. as mentioned you are looking around the 2000 year. if not already done you can expect to do valve cover gaskets cam seals cam adjuster seals and timing belt.The valve cover and rear cam seals are not to bad but adjusters and front seals are a little more complicated. I would not recommend doing your timing belt this can turn into a disaster if you dont know what your doing. and also dont forget your not going to run to your local auto parts store and just pick up the parts you need. even on a simple brake job if you dont shop around for the parts you will pay 3 times what you should have. my local autoparts store it would have cost over 400.00 for front rotors I got them for 120.00 but had to wait a week for delivery.

One aspect not mentioned yet:
The time you will spend on this forum ….instead of … being with family or ..fishing!

In other words:

Do you sleep well?
An Audi ownership will change that!

I would not recommend an older A6. If you want something fun, sporty, with room, and that will not impact your time with your family, then get an Infiniti or an Acura. Heresy, I know, and the interiors cannot compare to the Audi but I think you would be better off.