I always hit up whatever thrift stores I can find for CDs, as 90% of the time I find the best deals there. I rarely, if ever, go to a physical retail store and pay more than ten dollars for a sealed disc, when I can get it used (and in like new condition) for less than half of that price. Of course, I always check their condition and there may be the occasional one with the artwork damaged or the disc scratched to hell, but most of the time they're in immaculate shape.
Examples from two months ago, when I was on holidays in July:
Abbotsford, BC - My aunt had taken me and my dad to a Goodwill that had a fucking huge supply of music. In total, I had grabbed four soundtracks: A Kid in King Arthur's Court (still brand new in its factory shrinkwrap), Dick Tracy, Let Him Have It and Schindler's List. All four combined for $6.50.
Calgary, AB - The Value Village on 58th Avenue, by MacLeod Trail. Found the soundtracks for Terminator 2: Judgment Day and Halloween III: Season of the Witch, both relatively rare and $3 each. A Nightmare on Elm Street I & II was there as well, which I
would have picked up if not for the disc being damaged.
Jam it back in, in the dark.