Value of Colt Preban lower?

[extremist]

Hope it's okay to post this here. What's the value of a Colt Preban Lower?

Markings: AR15A2 Sporter II SPxxxxx S/N

Here's some pics:

http://www.lenaburgs.net/images/Colt/ColtAR15Rec1s.jpg

http://www.lenaburgs.net/images/Colt/ColtAR15Rec4s.jpg

Thanks,
James