Unfortunately modern cameras don't take the old threaded plunger type of cable release. So, unless you are able to make one, you'll need to shell out for a proprietary electrical model - this is my second Pentax model, as the other one I have only works with film cameras.
That complaining aside: you'll need a cable release or remote for those long shutter speed shots - night time, fireworks, even portraits and so on. You could get by if you set the camera self timer to 3seconds delay, that helps the vibration die down, but that won't work if you want to use the B speed. Using a cable release and a good tripod makes a big difference in picture quality.
For the other traditional use of a remote release - self portraits - the length of the cable is a bit short. Pentax does sell a wireless remote that's useful for that purpose - as well as the tripod slow shutter speed need - but the wireless uses a tiny battery.