Cluster Jewels introduce a brand new way of building your character and are a great addition to the game in general. Pricing them can be kind of tricky in a trade league, especially if you are not an experienced player. Some of the new notables are very powerful and are chased by many exiles. Some of them are simply broken, like Purposeful Harbinger, the one mentioned in this official post.
When it comes to pricing Cluster Jewels we have to keep several things in mind. The most important part is the base, since everything else is pretty much easy to re-roll by using Orb of Alteration or simply Chaos Orb spamming. For example, if you are playing an Impale build, you really want Deep Cuts, which provides 1 additional Impale applied on targets. What you should be looking for is a Large Cluster Jewel with as few small passives as possible. This will allow you to spend as few passive points as possible while passing to get your notable. Certain notables are associated with the implicit of the Cluster Jewel of course. You cannot get a Spell notable on a Cluster Jewel that provides “12% increased Damage with Bows” for example, which makes rolling the desired notables even easier.
When it comes to pricing these Jewels you should start with the base. Some Cluster notables only roll on bases iLvl83 and above, so those should be priced higher. Cluster Jewels with 8 small passive points should be priced way higher than those with 12. If you have a Cluster Jewel with a good notable combo it will of course cost a lot. When you have these pre-rolled ones simply look for similar on the trading platforms and price accordingly.
You can get a good idea of which mod can roll on every base here. The link is for Large Cluster Jewels and you can easily select Medium and Small in the options above.