I simply want an aux input....oh and cheap on my RNS-D

[Hiltoa]

I'm running a Connects2 USB interface (Which also has an Aux socket) on my RS4 as well as a Phatnoise - the USB piggybacks the CD changer cable and is the default CDC source, but if you switch from CDC to CD then back to CDC the stereo switches CDC source to the Phatbox. All this means I have the choice of Phatbox, any number of USBs containing 6 albums with up to 99 tracks or my 16Gb Ipod.
It'll do for now.

The Connects2 kit (CTAADUSB003) was around £60, and the unit fits perfectly in the undertray below and to the left of the steering wheel. Dead easy to fit as the undertray is open at the upper rear so the leads can be run straight to the stereo with no cutting or fiddling.

[Mr V10]

I did something similair to my car (RNS D). See here for more details http://forum.a8parts.co.uk/showthread.php?t=238