Well, those don't appear to be astounding sample shots, but the price sounds like it's about in the ballpark. I'm not too familiar with the going prices of the various models, but you can see the Lens reviews sections right here for some details.
Here's the version you're looking at, I think:
Sigma 30mm F1.4 EX DC Lens Reviews - Pentax Third-Party Lens Review Database
This thread may end up getting moved to the Lenses forum, you'll probably get more answers there.
I understand the HSM feature isn't on the Pentax versions of that lens anyway, so you don't need to worry about that, afaik, ...whether or not the newer version is better in other ways, that's best left to those with firsthand familarity with those models.
Also, btw, don't overlook the new DA 35 2.4: not what I'd call a terribly fast lens, but the image quality's great, and they're cheaper and smaller and lighter, which could be a nice combination.
I also like my Sigma 28/1.8: it's even bigger than the 30, but it has qualities that are useful to me personally for it. (like, good for film, is particularly nice with sharpness across the whole frame (as is the new 35) ..which is a very good attribute for me personally, because of my style with wider lenses: I like to put my subjects over there.
) Twill do, at least till I can lay hands on the Pentax Limited 31, which is very expensive but smaller and awesome.
Anyway, hope that helps. There are quite a few options out there within your budget that are quite nice.