Originally posted by Kitty Radio that does P-TTL are probably too expensive?
I am not aware of any radio solutions that use P-TTL. You can use the Pentax wireless, (which is optical) using either the built in flash or a hot shoe flash that can act as a master to trigger the remote P-TTL flash. Not all P-TTL flashes can act as masters so be cautious when buying. Or you can use the wired solution as suggested above. Or you can fore-go P-TTL and use one of the many manual flash triggering systems available.
For some additional information on using flashes check out
the strobist site. It really depends on what your needs are. If you are setting a static shoot, where things or models will not move much and the lighting will not change as in a studio then manual works just fine. P-TTL is better if conditions are changing a lot or if you are not willing or able to fiddle with setting up the manual flashes.