It's not easy to add smartphone-based infotainment to your existing car, especially if you prefer Android Auto. Many aftermarket head units are either devoted solely to Apple CarPlay (like Pioneer's AppRadio 4) or mind-numbingly expensive (such as the $1,400 AVIC-8200NEX). Sony is aiming to fix that. It just unveiled the XAV-AX100, a receiver that offers both Android Auto and CarPlay for a reasonable $500 -- even the relatively frugal AppRadio 4 costs $600.