They are expensive...all frames are, pretty much. The only exception is cheap frames from Walmart for standard-sized items (8.5 x 11, 11x14, poster, etc.). It doesn't help that a lot of the stuff for old games (the mini-posters, etc.) are all non-standard size. Last year I bought some custom frames for a few things, among them the "Now You're Playing With Power!" poster from the NES and some maps for PC games (Icewind Dale, EverQuest), and it cost a couple of clams.
But they look good on my wall and y'know, it kind of makes me happy looking at them. These CDs - looking at them brings back happy memories, times when I'd open that off-white CD tray and place the Starcraft CD in there, listen to it whirr, and then log on to Battle.Net. Or AOE2, or Deus Ex, or whatever. Those games were a magical escape - a real bright spot during high school and college experiences that weren't the always the happiest times in my life, despite all the great things going on I could have appreciated (but didn't). You're right - the frames are worth more than I paid for these items, in some cases, and because I haven't saved the boxes for them it's probably more expensive than they're worth today. But I think I'm starting to come around to the idea that the value of having them on my wall and being able to look at them exceeds the resale value, at least for me. Maybe I posted here to get feedback, think out loud, and talk myself into it...and I think I have.