I imagine the secondary market price of any 3rd party item would be most likely affected by how many this hypothetical group manufactured. If the supply was high enough, the price would stay down.

That's the problem with third party companies though.They don't have huge manufacturing factories to make the supply they need,so it's usually a low supply.Look at Fansproject.One of the most popular third party companies for transformer fans and they still can't make enough supply.They usually sell out in a week,if that.

He is goin for that much? Really, I havent seen him over $100 in forever.

As far as sentai would go, I'd buy power up armors/pieces only.

Maybe also cockpit/control panel (whatever they're called) as well. Like Gokai Silver's Darin, Shinkenger's podium looking thing, Kyoryuger's base/platform, etc.

If we're talking effects parts, then yes I'd be in on at least some. Outside of that, I'm not sure.

I don't know much at all about third party G.I. Joe or MotU stuff, but with the larger third party Transformer items, those are designed to transform and/or partsform around an existing figure. How many times would that be called on for a third party Figuarts release, especially if it's a human(oid) figure that's attempted? I could see an expensive, say, third party Auto Vajin; actual third party Riders/Rangers/etc. (if attempted) are hard to imagine approaching the price tag of Protector or other large ($100+) third party Transformers unless they treat like more like SICs and include a ton of swappable parts like for the alternate Rider forms.

Third party "upgrade" sets for Figuarts, I would think, fall more in line with the price for weapons or parts upgrades for Transformers; still expensive depending on who you're looking at (CrazyDevy is way up there, others are more modestly priced) and what's offered.

(I admit, though not directly on-topic...this has made me think of third party Sentai mechs.)

Yeah, outside of effect parts Figuarts is a line that's so all encompassing as it is that I really don't see a need for after market add ons.

I would say No. Since the accessories in the s.h.figuarts up to now are mostly enough comparing to the shows, I dont think I would pay about may be 1/3 or even 1/2 price of the figure for just an item of that figure.
But if they are effects like explosion, beam or effect impact, I am interested to buy some.

Others have mentioned effect sets, and i agree that would be cool, but i could easily also get behind battle damage sets. Helmets with pieces of visor missing, broken weapons etc. There are also few things that do seem like they're missing, Silver Crow could use a Gale Thruster for example.

I at least think it'd be cool to see unhelmeted Power Ranger/Sentai heads become a thing.

3rd Party people for Masters of the Universe Classics basically focus on alternate/new heads for figures as well as occasional new weapons.

So I could see someone do something like that for Figuarts. Maybe make the heads realistic or like the Akibaranger heads shown on the thread earlier 'anime' style depending on what people would go for.

If the upcoming Tricera Ranger/MMPR Blue Ranger does not have a long version of his lance, I could see someone do a longer version.

Figuarts are that expensive because they already are high-end collector's items. Using the Transformers example, the average Masterpiece figure costs around $130, and FansToys' (I think that's their name) Quakewave only costs $150. And I'd rather have 3rd party articulated Megazords that transform than Figuart accessories.