Use iTunes Match to upgrade your older purchases to higher bit-rate DRM-free music and then upload it to Google Music for free. :)
How to upgrade tracks to iTunes Match, fast
by +Jason Snell
Macworld.com Nov 14, 2011 8:35 pm
"So you’ve bought iTunes Match, which gives you access to shiny new 256kbps AAC versions of your audio files. But by default your iTunes library is still packed with your old files. So how best to upgrade all of those old files, in place, to the new versions?"
Hat tip to +Danny Silva
for the link. I went through these steps this morning, and left iTunes downloading the upgraded files. When I got back to my computer this afternoon, Google Music was automagically uploading the new tracks. (Note: This tutorial doesn't explain how to setup Google Music - you'll need to do that independently. It was already setup in my case and worked perfectly... though I may have some duplicate songs in Google Music though because of this... I'm not sure if the duplicates were already there.)