There isn't really a going rate as it's technically a discontinued card only used by system builders these days.I got mine for 50 or 60 back in 2006 though...
I can't compare it to the asus as I've never used one. In terms of pure sound quality you would probably not tell the difference unless you are using hi-end speakers and such. The gaming support on the creative support I think will be better especially for gaming with headphones because of the cmss -3d virtual headphone functionality.
AFAIK asus' technology is dolby based which means it is geared at music and films etc, and I know it supports dolby headphone which makes music on headphones have a much better soundstage. Creative's is homebrew it works ok for music haedphone listening and well for films I've found, very well in games. Feature wise it is much better than the audigy