They are changing hands fast as they filter into the market. There are only 5000 of the special edition M17's and around 4000 of the surplus M17's so that's only 9000 military M17's out there. As soon as they're all in the hands of collectors they will be scarce and the prices will likely climb.
Having shot mine I much prefer my Glock 19X or Beretta M9A3 because they're more accurate and shoot better, but I'm still glad I got the Sig M17 because it is the current issue sidearm of the US military and I don't know if or when they'll sell any more.
You can always buy a civilian M17 for around $600 and it will shoot the same but it won't be "the real thing".