All up I think it cost me ~$500-$600 so it's still not super cheap. I'm sure with some good scouting you could do it for a lot less with found timber.
Step 1: Google Sketch-Up Modelling
You'll need to get this program if you want to really look at the model in depth. I've included the .SKP files so you can see exactly how it's been modeled. There are measurements for everything on the models and they are all drawn in the size they needed to be when built.
From the model I worked out that I would need:
(240 x 45 x 2480) x 4 - For the top and sides of each side
(240 x 45 x 1360) x 6 - For the bed head and the foot
(195 x 45 x 610) x 2 - For the sides of the bed head