I purchased a Metra FMMOD02 wired FM modulator, a pair of antenna adapters, and wire connectors. Unfortunately, it sounds terrible. The signal is strong with little hiss and decent dynamic range, but turning up the iPod or my laptop caused it to sound overdriven and distorted, and the Infinity radio couldn't be turned up high enough to compensate.
Oh well.
I probably spent a total of $25 on the project. The Delphi modulator I used years ago sounded great. This was not so great.