There were 2 in the market place reciently in the 300 - 350 range with a grip,
the 200 quoted seems about right for a body only depending on mileage (shutter count)
I like you bought an *istD when it first came out.
I would never sell it, because although 6 MP is not the same as 10, 0r 14, or what ever pentax comes out with next, 6 MP still makes stunning photos.
Don't believe me? see below
https://www.pentaxforums.com/forums/106132-post4.html
It also does some things much better than my K10D, specifically it has true TTL flash metering, (the shot posted used a 300F4, plus 1.7x AF TC plus TTL flash) and as a result, I can do flash photography with my K mount (Non A lenses) of which I have 8,
It also is good in low light, and makes an excellent back up to my K10D.
You may want to re think your own situation, spend 30-100 on a split image and go play with manual focus legacy pentax lenses, they are great, and a lot of fun.