Aux in on an '04

Well I bit the bullet and ordered a Xenarc screen for a car PC setup in my Prius, now I need an auxiliary input connector. In the ideal case such a thing would mimic the MD changer or similar and provide an indication of which steering wheel buttons were pressed though this isn't vital.

I was just wondering what the opinions were on which systems were the best for this type of thing? I've heard bad things about DICE from around here, and Vaistech is slightly too pricey for my tastes ($400 AUD - almost the cost of the screen inc shipping) so is there anything that won't break the bank quite so badly?