aside from weight/bling factor, i think the main difference between newer sram shifters and older ones is the zero-loss shifting, and whether the feature is on both shifters or on rear only
in sram's own words...
Zero- Loss simply means, well, zero loss—when you push on the lever, for an upshift or down shift, the cable is engaged instantly—zero loss of movement. There is no middle-ground where you're waiting for the shift to come. Gear changes are instant and precise
there're both for sale and wanted sections...viewforum.php?f=23
price probably reflects their nature - shifters are safety critical items (imagine no brakes) and they have lots of components, which have to work precisely for consistent shifting, survive the weather, bumps and scrapes, brake operating forces etc., and continue to operate for a decent period of time without getting sloppy