The three bodies I own are the K-x, the K-5, and the K100d. The difference between the k100d and the K-x is night and day. It's a massive upgrade in terms of ISO, enlargement/cropping ability, and interface/processing speed.
The K-r is another good option for overall value because, as others have already mentioned, it has the same sensor as the K-x, but includes light up focus points in the viewfinder. I've heard reports that the K-r suffers from front focusing issues under certain indoor lighting conditions where the K-x would not, but I don't own a k-r so I'm afraid I can't comment much on that issue in particular.
Also noteworthy is that the K-r has a focus assist light that will come on when you are trying to auto-focus in dim lighting conditions. This is something that the K-x lacks, and was rather frustrating for myself when I was using the K-x.
Bottom line, would I recommend a K-x to a friend? Yes.
Are there better options out there at the
price you're looking for: No
For a similar price? Yes, the K-r
For a few hundred dollars more? Yes, the K-30
Here's a decent secondhand price on a K-x in new Jersey, about a 40 minute drive from Brooklyn. If you so chose to sell the lenses it comes with alongside your current k100d that you will be replacing, you might be able to come close to breaking even in the end.
Craigslist K-x for Sale, Elizabeth NJ