New Langsters cost $800ish
06 came with the replaceable dropout plates which is nice for people who actually use their bikes rather than just look at them.
I would pay ~$250 for a perfect '06 with a fork. Subtract ~ $30-40 since you are deleting the fork. Subtract ~$50 for minor scratches and dents. I think $125-150 is fair.
I really like my langster and am usually on the lookout for a good frameset which never appear on CL in my area.