My dad's had a couple of A4's now his last was a 03 plate and he currently has a 56 plate S-Line, great cars, high build quality, I wouldn't worry about the mileage I'd go for 1 or 2 owner cars, decent spec and well serviced, you'll be lucky to find any with low mileage for the price you want, my dad hands me the job of searching for cars for him each time, its hard work finding ones worth buying!