People saying its a staker or w/e. It probably is, but its not legit income/banks they already had. There has been a known bug for a few days now. Bug/Glitch/Dupe, whatever you want to call it; but it is injecting fresh non existent RSGP into the economy.
Video posted about it aswell on another thread. Some of you may know some Jmods, but there is an apparent post in the Mod section on RS forums about this 'glitch'.
Edit: That's why prices are dropping, its purely and simply dropping the value of RSGP.
Edit2: I also don't see RSGP going back up considering all the pre-existent stock of Gold dealers is still present, and this new fresh injection of RSGP into the economy is far far more than the playerbase. Meaning, there aren't enough new players coming in to fix this situation, to allow for the RSGP to circulate and eventually subside this surplus.
Edit3: How i know? I do ELO service for LoL, and the majority of my clients are ex/current RS stakers who only play the game for IRL $$$, and they are willing to pay basically 4X the amount i normally charge in RSGP. Asked them why, they stated what i said above.