[quote name='tangytangerine']You're thinking of GTA 3(which is $5 used there), San Andreas is $19.99 used there.[/quote]
I swear at Christmas time and into January it was marked $10. I marked it in my mind as a game to go and pick up later since I'm not dying for it, but I'd enjoy it. Then this thread came along and I looked it up at the GS site to see they're selling it for $20 used. Maybe this is a case of the site and store acting independently of each other, but if I had to guess I'd say the coming release of IV lead them to bump up the price of the older games $10 since they're more likely to be looked for (the exact same thing happened with Melee, which used to be somewhere between $25 and $30. It is now $40 there since Brawl came out).