If I'm not wrong, they can be broken down using the new Invention skill for a material called Fortunate components. These are used to make a particularly expensive ring that lets the wearer potentially find a super rare and expensive drop, which is why (g) robes (and most other treasure trail items) hover around 600k now.
The treasure trail items which are also usable on F2P worlds tend to be a bit more expensive too, as F2P doesn't have as much customisation / rare equipment compared to P2P.