Answered Rares, What's going on?

It seems as though prices of rares in the game are very unpredictable, maybe it's just me since I have not been following RuneScape as much as I used to. However, it really seems that prices of rares are a roller coaster. What rares, if any, would be good to invest in? A few party hats have fallen a couple hundred million gp, does anyone have a clue to why that is? Or were Partyhats inflated to begin with and came back to reality?

I don't know whats going on with rares but I would like it if you informed me. Thanks. Shane.