Since the prices of the original Pentax flashes have gone up like rocket (not only lenses), I think it's time to learn more about other options. I have found the following guide about Pentax P-TTL flashes, for both original branded and 3rd party options, highly recommended:-
http://pttl.mattdm.org/
(The Guide is being updated from time to time)
Read Also:-
Which Flash Units are Safe for Pentax DSLRs?
P-TTL Vs TTL - A Technical Brief
P-TTL Reliability