I have a 2013 A5 w/ 110K+ miles on it. Regular maintenance isn't bad. Just oil changes, filter changes, etc.
What's going to get expensive are the parts that aren't maintained but fail fairly consistently on these cars starting around 100K. Timing chain stretching, water pump leaking, ignition coil failing, shocks/struts, hard plastic coolant/oil parts that leak, wheel bearing, anything with rubber like bushings (control arm, engine mount, injector seals).
Less common are the turbo, fuel injector, high pressure fuel pump, blower heater, transmissions (if CVT). The other expensive items to mentally prepare for are electronics/computers that fail.
If you're going to pay a dealership to do all the work, then it's not worth it. If you can DIY and buy parts online, you'll save money but spend a lot of your life/time on earth cursing at the overly complex/expensive German engineering parts made in low cost EU countries/China.