So what's all this for? Before my SSD died, I was in the middle of developing an alchemy workshop. The workshop generates an amount of quests each day. I'm probably going to add a new type of quest section called "job quests", but these will be another source of income outside of slavery. These quests will ask for varying levels of potions and/or items depending on the difficulty. As you complete more quests, the workshop's level will improve, and you'll be able to receive more difficult requests for more flames.
I'm curious, does your mod intend to overhaul/rebalance the economy?
Because right now you can earn
so much money through slavery (fluid-producing slaves/selling demon slaves), and there's nothing worthwhile to spend it on after a few one-off purchases.
Earning more money becomes pointless very quickly, which in turn makes tasks that primarily exist to earn money lose a big chunk of their incentive.
What is needed are interesting purchases that are expensive, but don't ruin your game experience if you opt
not to buy them.
Ideally recurring purchases, or if they are one-offs, there should be a large enough number of them that the moneysink lasts several in-game years.
I think the spa was a (very small) step in the right direction.
It would be good to have more complex rooms that cost a lot more to build than the spa, have high daily upkeep costs (much moreso than the spa or any existing room), and offer truly unique functions and non-generic sex interactions.
Your workshop sounds like it could go in that direction, requiring expensive equipment to improve its level, and rare/costly raw materials to produce higher-tier goods.
And in return for that investment, it would offer some benefits that could not be acquired any other way, like buff potions with a higher active effect cap than hand-brewed/shop-bought stuff, or advanced transformatives capable of overriding demonic immunity to standard TFs.
However, it is still rather problematic how the existing broken moneymaking methods get in the way of any kind of moneymaking system added later (like your proposed job quests).
Multiple millions of flames per day via a fully-automated system (i.e. a stable of fluid-producing slaves) should never have been possible until
after the main quest was completed, and "just don't use them then" is a terrible non-solution. Better that they're rebalanced so they can be used without snapping the game in two (eg. scale the base fluid prices down a lot, and also add supply-and-demand that scales prices down even further based on raw volume of fluids sold in a sliding one-month window).
But perhaps it's outside the scope of the mod as you stated you didn't want to make significant tweaks to the base game.
So maybe you would be limited to adding more moneysinks to prevent the current "money is useless" state, but without touching the base earnings possible in the core game? In other words you would price everything assuming the broken moneymaking methods were being abused.