Trebuken's prices are probably fairly close. He is correct about his X-Com prices - X-Com is not worth anywhere near as much on PC as it was on the original PlayStation. Several of these games were also released later in "compilation" sets: the Ultima Collection, Might & Magic VI: Mandate of Heaven Limited Edition (contains Might & Magic I-VI), there were several collections of the AD&D Gold Box games...that drives down the price of some of the originals, even if they're in pristine condition, because it's a lot easier (and sometimes cheaper) for people who just want to play the games to get them all in one fell swoop by buying one of the collections. That's why those collections usually go for $100-200, easy - cheaper than shelling out $30 x 7 or 8 to pick up the games one by one.
Still, I'm sure Daggerfall and the Ultima games will probably go for a good price - they're the gems of the collection. The Power Dolls one is anybody's guess...I've never heard of it, either. Relative unknowns don't usually go for big bucks, at least I don't think...I'm not sure it'll go for the same price as an Ultima or Daggerfall. I know I wouldn't pay $70 just to try out a game I've never heard of. But who knows? Maybe someone else would, or wants to "complete a collection" of PC games or something.