A guy was trying to sell a beat up one like this on GB for a fortune a couple months ago. Maybe it was a M8. He came sniffing around here for info about it because he didn't really know what he was trying to sell -- or he was trying to circumvent the sales rules here, however you wish to view it -- and was less than enthused about how he was received. It was amusing.
Anyway, that's pretty cool. I wouldn't pay any more for it than any other M13 in similar condition. Maybe even less since it's been molested.