ITunes Match is $25 for a year. I'm pretty sure it's unlimited if purchased from itunes but but something like 25,000 songs can be uploaded not purchased from them. Except it doesn't really upload your actual files, it uploads your library list. When you stream or download to a new device it actually pulls from Apple's catalog in their AAC file format. In some cases this could be an upgrade to your original copy.
I'm going on my 3rd year using it and love it. Works great for me because I have 2 Macs, 2 iPhone (with wife), an iPad, and Apple TV. My entire catalog is synced across them all.
My only complaint, once while listening to a Beastie Boys album it sent a Match Box 20 song or something that I don't have on my library at all. I searched the problem and someone else said on a forum that they were trying to listen to the MB20 song and got the BB song. I guess those got crossed in their catalog or something. That has only happened to me with that one track though.