Instead of analyzing the cost to produce, we could instead analyze what a single orb is likely worth.
To renew your supply of fewell directly from the NPC, the cost is 100 gil per 1 unit of fewell. An orb gives 50 units of fewell. If the price of an orb is over 5k gil, it's cheaper to "fewell up" directly from the NPC.
As long as the price of orbs stays below 5k single / 60k stack, I can see this being an active item on the open market.
@Fairy.Bastion
The cost of making a stack of these with only NQ results, is indeed only 9786 Gil (with minor variation of the crystals necessary to craft).
You yield, as following:
NQ: 3 Fewell
HQ1: 6 Fewell
HQ2: 9 Fewell (unconfirmed, but assumed)
HQ3: 12 Fewell (unconfirmed, but assumed)
This is the price, if you buy the Colored Rocks at the Goldsmithing guild, for their lowest price of 1,288 Gil, when stocks are maxed.
However, I'm fairly sure, when Synergy hits in full effect, the guild stocks will be emptied and prices for Colored Rocks will top at 6,440 Gil a piece, making the price 30,394 per NQ stack.
So by all means:
Slime oil + Colored Rock + Catalytic oil <= 30,000 gil (depending on the market)