I recently bought a used copy on ebay for about $40. The price was kinda inflated because of it being out of print, but I've seen it go for over $60 before. Just be careful to avoid the chinese bootlegs though.
If you have teh cahs, best bet is to get it at http://www.amazon.com as they have it, and they never sell bootlegged anime.
If not, then it is ebay where you will have better luck finding it for cheap. Make sure you know what the official Iria DVD set looks like so you won't be fooled into the evil bootlegged ones.
Hey! That was my first anime! Wow, i can't believe someone actually remembers way back when Sci-Fi ran anime in the mornings. and then they took it off,