While shopping for my K-30 I was faced with same question. Here is my experience.
I shoot outside under sun (bike racing) so was looking for high speed sync (and PTTL of course) as a requirement.
After carefully studying
Feature Comparison - Pentax P-TTL Flash Comparison I narrowed down the list of choices to only those supporting HSS and wireless and reported to work with K-30 specifically (searching the forum helped identify these). Then I Googled those few models looking for deals. Thus came up used Metz 48AF-1 for $156.99 at amazon marketplace. I got it and after upgrading firmware to latest it works fine with my K-30 doing HSS while on hot-shoe and regular PTTL wireless workng off built-in pop-up flash.
Next step is make HSS work off-camera, so I'm shopping for a second flash that'd work as HSS master (so far used
Pentax AF360FGZ - Pentax P-TTL Flash Comparison looks like only guaranteed choice to work) while on hot-shoe (popup flash does not support HSS at all).
Since optical wireless range is very limited under the sun I've ordered
Aokatech radio triggers