It would not be considered rare but maybe uncommon if that makes sense. There were more small block SS cars than big blocks. The SS427 Z-24 option is considered rare.
Depending on body style, color, options, and overall condition, $2500 seems fair. Keep in mind, sheet metal for these cars can be very expensive and many other parts are very difficult to find. It will cost as much to restore this car (worth approx. $15K done) as it would to restore a rarer car worth $50K. JMO
To get more opinions from similar owners, check out
http://www.impalaSS427.com
[Edited by SS427 (04-12-2002 at 12:15 PM).]