The 8500 lists for $799. If you have it professionally installed it will cost you a few hundred dollars. The performance of the 8500 is ok. Once you start getting into the $600+ cost for a radar detector, spending a little more money is worth it. The Beltronics STiR+ lists for $1299 and is the top performing custom installed radar detector. Many retailers may discount the STiR+. I would contact BestRadarDetectors.net during regular business hours. He offers great customer services and is very helpful in picking the best radar detector for you.
I hope your A4 does not have radar assisted cruise control and blind spot monitoring systems.
