Military Payment Certificate (Series 641)

Here's a pretty good paper note find I had a while back. I normally don't collect paper notes, but I saw this in a pawn shop's display shelf for 2 dollars and thought at that price I had nothing to lose by getting it. From what I've found out, this is a Vietnam-era military payment certificate, the series 641 meaning that it was printed in 1964 and was the first of it's series. The note is UNC other than the fact that it has a slight crease down the middle. My guess is somebody folded it a long time ago, it doesn't draw away from the general appeal of the note that much. Not that I wish to let it go anytime soon, but I'm curious as to what these things tend to go for?

Here is a picture, the quality does not do it right at all in my opinion... but it's the best I can do for the time being.