Well those price increases were due to numerous factors. One big factor was the introduction of new rewards to treasure trail, meaning the chance of getting a Robin decreased. They increased the price twice (IIRC). Then there was the stupid price increase when Jagex had an update, and their update said "Hold onto your Robin Hood hats" or something to that degree and people played off that saying that they were to be untradeable. Of course Jagex meant no such thing and it was just a saying. Nevertheless, the price still jumped up. So unless something like that happens again, I don't foresee any price increases.