Nothing is hard to get. It's incredibly easy to camp any kind of dragons that drop visages and get yourself one. The same goes for getting an onyx, just doing a jad run would get you 2. Prices are created by the people trading the items, I'd say buyers have the most effect on them.
there are tons of items that got a bad price.
ring of stone (best ring ing) 700k
amulet of fury 700k-1m
dfs 3-3.5m
what could we possibly do to fix these prices?
1. lower drop rate of the supplies by alot.
2. add new effects to make these items more popular e.g. dfs spec or let onyx necklace boost obby mauler's damage?
3. wipe out a % amount of these items that are ing already.
Some items just need to have less sources. Onyx is a prime example, it's dropped from way too many monsters. Visage is fine as it is imo, for every visage drop I've had during slayer I've had at least 6 onyx drops. Stone is not the best ring ingame, vigour is. Dfs spec already exists, so does berserker necklace, buffing these items won't necessarily make them more expensive, it just buffs the items.
Wiping is never a good solution. It pisses people off and only temporarily helps the problem. Continued item sinks are the way to go.