Not tried em, yet you should be okay as long as they are Ritek, as the cube is very picky on the media. Others might work, yet you will get DRE (disc read errors at random points in certain games.
http://www.wcwmedia.com
They are UK based and the cheapest i've seen so far for Traxdata Mini's. I have over 100 games using those discs and they work flawless.